Hello from San Diego,
 Am I reading you correctly that you need a narrow case (front bolt pattern) unit for your car, and you have a wide pattern (front bolt pattern) case transmission?  I have some of those (narrow ones), but not 109% sure of your tail housing need.  I have a lot of these parts!!  Answer me about my question and I will research your need after that and verify  IF  I have the needed parts to assemble one I will let you know.
                                   Mike

Hello,
 looking for an "A2" balancer and water pump (428CJ) core or rebuilt and a 4-speed bellhousing.    Anyone here happen to have these parts... Or only one of them??   Can P.M. me with answers...
                                                                                             Mike

Hello from San Diego,
 I might have a spare one of those.  Will not have a chance to look to be sure until the weekend.   Can let you know afterward.
                                                  Mike

Hey there Stangman,
 I just based my thoughts on the performance and longevity aspect.  Thinking of when opening up the carb quickly with a smaller motor and a big plenum, there would be a considerable power bog at the start.  I know this could be compensated for some with a more aggressive accelerator cam.  Or a larger pump, but that could wash the cylinders more and could be a problem sooner than later.  To be clear as I can on that thought, I’m not saying in a thousand miles the combo would ruin the engine!  But it could shorten the life by 20,000 to 40,000 miles in comparison, in a longevity consideration.
I’m just keeping the conversation going for us to think about thus stuff.  And in all fairness, Jay’s book stated the most power a 390 made was with an old school Streetmaster with plenum work and a 1” open spacer.  That is an argument itself with my F-427 theory if you think about it…. That all said, the Streetmaster intake will not look original(!!) , and does not have the PCV hook-up provision.
                                                       Mike