This might obviously not work, and I searched all the forums and couldn't find an answer. But I was looking at a stock exhaust manifold for the 420A and it doesn't look all that low. I was wondering if I took a Mitsubishi style turbo flange and some kind of exhaust flange if I could make an adapter plate to run something like a 12a, 14b, or 16g on a stock exhaust manifold. If this is a dumb question someone just let me know, but i've never looked at the stock manifold in person without the heat shield. Anyone think this will work or has anyone ever heard of someone doing this before?

How can you ask if you never looked yourself. Not to be blunt or rude but the main part of making our slow cars fast is trial and error and more trial and error with a bit of investigation every now and again. But answer your question yes it is possible but so is any thing. Have people cut the 4g stock flange and installed a 420a in its place and used that as a turbo flange. Yes. But to my knowledge there is know adapter plate. (Probably cause premature cracking) You can do what I did, cut off the exhaust pipe flange and modify the square portion of the manifold to except bolts and bolt a 14b on it. But you will eventually have to look to see what I am trying to say. So get wrenching.

yes you can put a 14b on the stock manifold.
it will be held on by only 2 of the bolts though.
will it work? yes
Has it been done before here? yes! back around 2001 it was a very viable option for the use of some of the 1G turbo parts.
is it a good idea today? depends on the budget. you can turbo the car with a 14b for around $800 (more or less depending on what parts you can get for free) it also depends on your goals. High HP goals? not a good idea. with todays avaliability of good T3 manifolds you can piece a more common kit together from buyable parts and have little or no modifications to do.

if you still want the 14b, go to http://www.roadraceengineering.com/ and pick up the weldable Mits flange and weld it to the 420 manifold.