rough idle V12

Hi folks, I'm new to the forum, but not new to wrenches. I've stumbled across a problem I'm hoping someone can help me with. I have an 83 XJS with a blown V12 motor and I just installed an 85 XJS V12 motor in. I switched over all the electronics and intakes from the previous motor.

Now my friend and I have been trying to get it to idle with only partial success. The only way we can get it to run smooth is to run a vacuum pump onto the computer in the trunk set around 22. The engine will only produce a vac of 19 at best. We cannot seem to find any vac leaks with one possible exception which is the crossover tube. The sleeves in the intakes that the hoses attach to have come loose, but I've glued them into place and will make sure they're sealed in the morning.

Still, they fit close enough that it shouldn't have caused that much of a leak. Intake gaskets are new and sealed, every vac line has been inspected including the one running the length under the car. Timing has been checked, rechecked and checked again.
Any suggestions?