Ford F700 under repair

Hi, I am working on a 1991 Ford F700 with a multipoint injection 429 cubic inch engine. It has been boogied big time, the injection has been disconnected and a Holley 750 grafted onto the intake manifold. It still runs standard exhaust manifolds, but all the EGR has been removed and the ports plugged.
The truck arrived into my w/shop with low compression and very little oil pressure. I removed the sump and found traces of white metal stuck in the oil pump pickup screen. I have decided that lack of servicing is the main problem as the oil filter is clogged solid.
My question is - if I leave the injection manifold on the engine instead of changing to a Edelbrock performer manifiold to suit the carb, will I run the risk of overfuelling and washing the bores? I have a sneaking suspicion that could also be one of the contributing factors to the engine failure.
I have stripped the engine right down, and the 2 rear big end journals have zero bearing left and have scored the crankshaft.
I am about to grind the crank, line bore the block, replace the 2 con rods and run 20 under mains and bigends. The pistons will do another turn, but will re-ring them and hone the bores.(surprisingly they are in very good condition) :confused: Does anyone have any experience with multipoint intake manifolds having carbs grafted on and how badly the fuel/air mix is distorted??