I've never measured "down in the hole" height, but my favorite combination is a 1968 or 1969 shortblock, which had an advertised CR of 9.25:1 with open chamber heads, floating pins, and lighter weight rods than 71 up teens. Add a pair of the 302 casting heads, or a pair of 1967 273 or 318 heads, either one is closed chamber, although the 67s are a few CCs smaller chamber. Port match the heads to as close to a 340 intake gasket as prudently possible, blending in about an inch and a half. Put a cam that is reasonable for the car weight, gearing, and intended use in it. Top it with a decent intake and either 68 to 70 340 manifolds, 95 and up Magnum manifolds, or a set of headers. The 95 and later Magnum manifolds are slightly larger than the earlier Magnum manifolds, and have larger outlets. Timing might need to be conservative for 89 octane, but dialing in the amount and rate of both vacuum and mechanical advance will get you there. These engines really wake up with some compression, more so in my opinion than flow. We put together a similar combination for a friend's 86 M body Gran Fury. This friend had owned more than a dozen 340 A bodies over the years, and his exact words were "that damn thing is amazing! It runs as strong as any 340 car I've ever owned"
