dude your best bet is to get a FRESH EMPTY LS Block and start from scratch !! I can give you a list of do and donts and what you need piece by piece ! If you wanna go forged it makes it easier but if your going with stck internals youre gonna encounter some weak points !. I have A LS Block and Balanced crank with GSR Pumps I was doing LS Vtec but decided to sell my car or go with a B20 instead. Basic Build up for LS VTEC is simple,

B18B Block perfreably with air oil seperator
B18B Crank
p72 Pumps ie. OIl and Water
Then internals youll want these
Crower Rods Stock length
and your choice of pistons weisco, endyn whoever you want bore is up to you ! Stock is ok but ihgh boost youll want sleeves or some sort of block guard like STR's
But if you want larger bore ad stroger block B20 with a closed deck is better and also you use LS rods BUT use B20 Pistons and i think wesico makes the VTEC version.
Clevitte or Top line bearings !
Then you have to get a VTEC head Preferably Type R or B16 B16 is closer to Type R than the GSR is !! But all will work none the less. after thats all done you can handle like 15-19 psi easy !! but build the head if you dont want your head to fall apart at like 9k rpm !! it depends on your wallet how fast your motor will be and how long it will last !! If you need parts i have shit everywhere let me know !!