Waking up the ZZ

[pdawg]

Hey experts! Looks like spring is here so I need some advice on a problem I put my '72 Custom Deluxe to bed with last fall. My son & I completed an engine swap for the aforementioned GM ZZ383, but I haven't been able to get her running to its potential yet. After over carbing it I put a Holley 670 Street Avenger on it. I'm not a mechanic but I have played around a bit over the years. I completed it with a Mallory HEI distributor. It has no vacuum advance - per GM so I've timed it as per spec at 10 degrees, with the distributor bringing in the rest. When the engine is hot ( which is barely into the normal range) - it starts to run rough & if I put it in park it revs up considerably & will diesel if I shut it off. One would think vacuum leak but I chased the usual suspects ( carb base, intake manifold) with an unlit propane torch looking for an increase - to no avail. I am using an Edelbrock Airgap manifold. I've replaced all the vacuum lines including the brake booster line, but still no joy. Any tips would be greatly appreciated. Also - once I do get this solved I've been thinking of changing to a posi rear end & 700R4. Thinking 343 gears should wake it up a bit but still not rev too much on the hi way. Any suggestions re: brand of posi, parts required, or tips regarding this would be appreciated. Thanks in advance!!
Perry