408 Stroker Build Suggestions

How much is a used LD340 worth? You're saying I'd come out $100 ahead by selling it to buy an RPM? I had no clue the LD340 was really worth much, it just came on my Roadrunner (which I didn't even realize until after I purchased it, I thought I was getting the stock two barrel under the air cleaner and was very pleasantly surprised).
IMO round off the sharp edges of the center divider, stick a 1" open phenolic spacer, and block the exhaust heat crossover on the LD340 and save your money. Port match the intake and heads and clean up the ports regardless of what head you run. The Js and Eddys will definitely improve with cleanup.