You need MS if you want to get the most out of your build NA or boosted. Look at all the NA guys and see what they are running. Almost all of them are on MS or they are running some other tunable ecu like the afx. You can build a 2.4 using the stock fuel maps if you want, but you won't get as much out of it. To make the 300-400 HP you're looking for though, MS is pretty much a requirement. Stock fuel maps won't get you anywhere near there. You might be able to get there with an sfmu and a safc, but it won't be much cheaper and won't be able to tune as finely.

The combination I'm looking at going for is a 1:1 afpr, MS1, a Walbro 255 and larger injectors. That setup will work whether you are NA or Turbo, depending on the injector size. You just set the 1:1 and the fuel tables in MS differently since you won't make as much power NA.

Good luck with your piston/rod search. Take your time, plan everything out and I'm sure you'll do fine.

My build: verttuner.com (hosted on my blog)