Here's a motor question

Not sure if this is the right forum but here it goes.

Say I have a late model 258 (85 or 86) out of a laredo and tear it down and rebuild it with the plan to put one of those mopar FI's on it. The plan is to rebuild the jeep it came out of and then put the motor back in FI and all.

Questions: While the Jeep is being finished. Can I just slap an earlier manifold, and carb (73-79) on the motor, throw it into my 74 and break it in for a couple months? Then take it out put it into the 85 or 86, install the fuel injection and be off. I want to say later heads on the mid 80's motors will not allow this. Is this true? If so what is the cutoff year for manifolds? Another idea would be to put an aftermarket manifold and carb (basics, no smog) and break it in that way until the other Jeep is ready. Are the later motors dependent on smog equipment to run smooth or will this plan work? This may sound strange but any help??

 

AFAIK, all the 258 heads will accept all the 258 manifolds. I have '85 manifolds on my '77 engine. The only problem was I had to notch the '77 PS bracket to clear the '85 exhaust. You can put all your '74 externals on an '86 long block with no changes.