If I hear you right, the only changes were the 1050 pistons/barrels and the heads were modified?
Were the heads shaved to achieve the 12:1? How were they modified? What specifically was done to create the squish band?
I've got a 77R100S that supposedly has a 1050 kit (so I was told by the PO, though there are no receipts to prove it) and it's been dual plugged. Supposedly it's got higher compression too. With mods to the advance I've managed to get it running pretty good with minor pinging under hard accelleration but it would be better to eliminate it altogether.
It seems that you have the answer!