Looking for Member Chevytech

[72CSTC5]

My dad bought an 83 gmc that had a blown motor. Someone had put in an 95 suburban motor so we pulled it and went and bought a crate general motors 350 engine and installed that. Put new plugs and wires and rotor. The problem is that the truck has a miss at idle. He has all of the vacuum ports that he is aware of blocked off. Any suggestions on where to look next. Could the distributor be in one tooth off causing this miss? Thanks in advance for your help.