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Hear me out guys, read what I think he should do, I'll explain....
Milling the cylinder head isnt bad, but too much can hurt timing, if too much even cam gears wont be able to get the car to respond at best, they only offer 10 increments adv or ret(my car's cams are little retard side cause of milling)so watch out!. If you are going to go ahead and pull your pistons out to look at the piston rings, just go aftermarket pistons and raise comp there, mill the head .010 or .020 thousands just to flatten the surface and also to get some compression. I have somewhere between 10.5:1 and 11:1 comp ratio and I barely survive on 91 octane in AZ (wiseco 10.5:1 and shaved cylinder head). Now for the P&P the head, carefull, you said you want streetable, so tell that to your head porter. Being honest with your setup is the key to making power, tell your head porter straight up and say "Hey Mr.whatever, I want something done to my cylinder head, I want it to be streetable but to get some power out of it, like maybe 5 or 10 hp, what can you do?". Most likely he'll ask about your setup you have or plan on going to do and he'll do something about the ports that'll match your needs, he'll even machine it if your telling him your gettin step up cams. Most likely tho, they'll just do a vavle job, match port the intake and exhaust and tell yah to raise compression, cause there isnt much to be done anyways to these heads, if the claims are true that our heads are straight off of "lotus" engines. Valve job , 3 or 5 angle doesnt matter, more the better, will help unshrouding (tulip shape airflow around the valve flowing more air) at its earliest lift of the vavle, !!!THAT RIGHT THERE IS THE MOST IMPORTANT MACHINING WORK FOR 4 VALVE HEADS!!!! Think about it, your intake valve starts to open, then to .080 thousands lift , then .100, then .150 and soo on to max lift, then it makes its way back down through those numbers and then close. If the valves are going to open most of the time overall at those lifts, you'll flow much better overall with valve job!. Porting will help airflow at more higher lifts or even to max lift in most cases, however, your trading velocity for volume, meaning if your going to do some extreme porting head work, gotta rev Higher to keep up the velocity. Your also going to need your "Combination (exhause side mods, intake side mods, cams)" to work at high RPM and you'll need to have a car that "CAN" get to higher RPMs, you're screwed if you got a head ported for 7-10K RPM flow range with stock cams,tb,intake mani. Car cant breathe at higher RPM's cause of stock mods, and cant flow cause of super ported heads, lose-lose combo =(. From what I've read you wanted to keep your Street RPMs, correct? for streetability? (Low to midrange RPMs), and I doubt your all "close to stock power" mods can flow serious amounts of air at higher RPMs. You can machine the ports (valve pocket area) maybe alittle bigger to help unshrouding, but I doubt you or you're head porter has access to a flowbench (or afford to get your head flowed) to see how well your flowing with the porting hes done at and lookin at results at various lifts. As for Valves ,I have no clue about bigger valves, however....heres something to think about. Another best way to get unshrouding is to bore bigger on your cylinder bores. Valves wont flow well when you have it right next to the cylinder walls or head gasket, so you should bore bigger, like .020 or .040 thousands over. Hey does this sound familier to anyone? yup, its from F1 racing (I think of those cars the kings of 4 valves all motors, or Hondas and Toyotas =P). Look under the head of a F1, the valves are miles away from the cylinder walls, all for airflow. Since they have 4 valves cross flow heads, and soo do we, we CAN apply that method of boring big for unshrouding!!. Now onto cams, with cams go with mild cams, (heck I dont even have aftermarket cams and my head is machined for em) there streetable and will offer power. I know they all cost the same (I think)when they offer in stages but there is a reason, an important reason. You're going streetable? go get streetable cams or stage 1, there meant for your set up and might prove better wiht a massaged head! You got some work done to the ports and you got the intake and exhaust mods for higher RPM power and flow? go get stage 2, your going to lose low end, but thats the nature of your beast if you have the setup for high RPM power/hardly streetable car, right?. Got a turbo you put on your car that was N/a before? get Turbo cams. When it comes to turbo and Nitrous and N/A cams, they is certain Intake/Exhaust Ratios (especially the cylinder heads), lifts might be different, yaddah yaddah yaddah. Thats why some people might throw in like Stage 5 N/A cams on there turbo cars that was originally N/A but it runs like SHIT!.. Stick with the cams that are meant for your Set up!. As to your nitrous question 50/75 shot? I dont know how well stock internals hold up wiht high compression and Nos, sorry, ask someone else on the board about that.
K, I think I've said enough, and dont worry, I've already tried some of the mods I just talked about, they're workin great! Valve job, raise compression, step up cams, (and if you can, bore bigger for your cylinders) throw those in the mix of your setup. You will definatly have a "streetable" car and still hit low 15's (maybe 14's). When it comes to makin a street/strip or full blown race car, match the combination for the nature your car is going for, enjoy!
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It refers to the number of different angles cut into the valve and valve seat. They cut matching angles into the back of the valve face and the seat in the head that the valve closes against. These cuts allow the seal to be closed better, but also to ensure uniform air/fuel flow into the combustion chamber. The more angles, or cuts, made, the better the seal and smoother the flow. You got your 3 and 5 angles, then there's the full radius, where they match both surfaces entirely to give the best seal and flow possible. I've got a 5 angle and was told that a full radius would be great, but it wouldn't do a whole lot more for my setup.