"""  If I put 1.9L heads on a 2.1L, (which is being upbored to give 2.2L),
then the effective compression ratio is now about 9.5 to 1"""

Which brand of pistons Curious? i was about there with my EX Tornado red
engine, maybe a bit higher. your CR depend on the pitons dome as much as the
head CC... are you using the same sleeves.

For sure, i would not use old head if the CR is higher. I don't trust them
no more.

Ben