1991 Chevy Truck Engine swap issue

Engine Performance problem
1991 Chevy Truck V8 Two Wheel Drive Automatic

Ok here is my problem. I took the 91 350 out after my wife blew it up and swapped it for a 350 block and heads from a early 80s 350. I put the tbi intake on the new block with some modifications (widening out the 4 center bolt holes). Now we can not get the truck to run correctly. It sounds as if though the motor has a miss and also has no power. We can take the brake booster vacum lhose off and it will idle. But as soon as we hook it back up the truck dies. The timing is dead on accurate. I am at loss with this thing now. This is also our only vehicle and now has cost more than I think it is worth. Any help is appreciated