Bob, can I ask the question another way? For the engine example given, if a person were buying a new cam in any event, does a solid grind give any performance advantage over a hydraulic grind of a like-grind, EXCEPT the increased rpm that a solid lifter allows? To get the advantage of the increase in duration, can't he just order a hydraulic cam ground such (such as OGTS's Torquer Cam) and stay with hydraulic lifters (new ones, of course)?
In other words, is it true a hydraulic lifter pumps off at around 6000 rpm, but the solid lifter will go much higher, so long as OTHER limitations aren't reached first (such as weak valve springs causing valve float, or intake/carburation limiting high end breathing, or crank and/or rod failure, etc.).
Based on the example given, I suspect that this engine seldom will see more than 6000 rpm, so would the solid lifter (and cam ground to same) provide significant (if any) performance gain? But it will require more maintenance and somewhat more associated noise.
Does that sound right?
As for the '70 head, it will fit the later block just fine. The later (post 'mid '72, 12 bolt head) chain case on your block is designed to be flush with the block deck and then bolted to the head with the extra two bolts that the earlier head doesn't have. So two things to watch for:
1) If you get the block decked, the chain case must also be decked the same amount (I did mine at the same time) or it will stick above the block deck.
2) Since the later case and block are flush, you must use the later head gasket (without the cork gasket at the front), and just put RTV sealant in and around the unused holes in the chain case.
HTH (pending RallyBob's comments on my solid cam questions)