[Jac Mac]

Wayne, you mention in post #7 that the old heads had a couple of worn guides- they wouldnt happen to have been from cyls 5&6 would they, if so the rings/bores on those cyls may be glazed, also check the stem seals those cyls & inlet rocker studs if they go thru to the port for sealant.
Leak down test 'might' help, but another way is to buy/borrow a 7mm or 10mm headed flexi lead TV camera that hooks up to your lap top, you should be able to get that down the #5 intake runner ( #6 might be a challenge with that intake manifold ), very handy tool to have these days, you can get these in thru a 14mm plug hole for a look inside the cyls as well ( just dont try it on a 'hot' motor), wish we had this stuff back in the 70's, but didnt have the $$ they were asking for borescopes back then.