Eric,
I have installed 2 ZZ4 crates (actually the same one twice) in a jeep and then a 78 p'up. It is much more complete than the 300hp HO and is well worth the extra money. It is the newer style with center bolt covers and one-piece rear main and should bolt up to your AOD easily. It also has some cool features like accepting the smaller hi-torq starter (for better header clearance) and the newer accessory brackets which allows for a serpentine conversion.
The pain is that you will likely need to purchase or modify your accessory drive, and depending on your carb selection (I would do the newer Edelbrock for its idle quality) the mixture adjustment is tricky. Also, despite making 350+hp, the engine is somewhat top heavy with the .520 lift cam it comes with. It is not a slug by any means, but you will have to get used to it. You will, however, get an impressive passing gear once it winds to 3000+ rpms.
Given what I learned, I would definitely go that way. You could not build a new engine to that power level and reliability for the $3K price. You could spend that screwing around with a TPI for your old 350 and never get the same results. And the ZZ idles almost as well as stock. Amazing.
Good luck on your project
Steve - 90 Warpig, SW Michigan
