Muscle Motors' Steve Dulcich (whose forgotten more info than I know) states that the later heads 452's etc are far easier for the home porter to improve on as opposed to the earlier 906/915 though 452's would need to b thoroughly crack checked & I would get the MP templates & port em (lot of gain/not too much work). Might go to MM archives & read his articles. Been a few reported probs w Indy's stuff but prob no more than the norm (& maybe even less) than any rebuilder as you (most of the time) only get the bad news on stuff here. I ran a set (SB's) of their rebuilt ones & no issues. Iron heads need alot replaced/reworked to get em right but as you said alum ones are $$$ plus need to b checked over after you buy them. Myself in your case w a mild 440 I'd do a bare bones rebuild on your 346's & save for a good set later. dont remem if 346's had hardened seats as they were close to the changeover on that & we know how Ma was on supposed published changeover years