I've done plenty of reading and no double need to do plenty more.
I have an '07 envoy, which is having its chassis and drivetrain swapped into a 1956 International Harvester Metro Van.
I have seen plenty of talk that the '07 stock ECU should be able to handle boost with larger injectors.

is there any tutorial, or video of someone who has already done this? I just need to get my legs under me to see if this is within my skill range, having never attempted programming an ECU before.

search 4200 on you tube their is a guy who has done a Boat load of vids on the 4200 and has done dynos as well race. I just can't for the life of me to remember his name.

Go to Tech-Tips and click on Vortec 4200 or PM efi-diy

thanks guys, I'll take a look

if you are talking about Nivlac57 looked through most of his videos, most use a early ECU and a minisquirt in parallel. nothing with the late ECU (that ive seen so far)
most others have standalone

https://sites.google.com/view/vortec4200wiki/home

lime-swap.com >>> stock ecu help

what are general thoughts on Turbo and injector size?
Wiki says 1000cc injectors and a GT3582 (I confused this with a T3 with internal waste gate)
spoke briefly with the guys at lime swap and I was told that injector size is too big and turbo too small.

considering 1000cc injectors flow 4x the stock ones, just based on horsepower output they would probably be overkill for my wants/needs
630cc units should be plenty capable of 400hp? and a GT3582 paired with it?

I run 630 cc and used to run a GT4088 - good combo. The 630 injector are good for 550hp and so is the 4088. 400 hp wheel on a 4200 is easy.

thanks for that, seems like I'm going down the right path.
now to replace the main and rod bearings on my engine.