Mike---I can give you a part of the answers you are looking for. I've
read somewhere that the "U" means the vehicle was shipped to the United
States. So far as there being three different (compression) heads, it
would seems logical that there would be three different head thicknesses
involved. The thinnest head would be the one with 8.5 compression ratio,
the thickest would be the 7.5 CR, and in between,---I don't have these
actual dimensions handy, but the differences I recall are substantial
enough to be easily measurable. Be sure your manifolds match the head
ports. I'd go with the thickest head as part of the engine buildup,
and machine it down if you're looking for more compression. And I'd go
with the block with the smallest bore, to leave room for future
re-bores.
Dick T
'73
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