Yeah, it had plenty of compression.
You could just keep it simple and set it up with the 66mm.
But, if it were me, I'd go for the 68mm+ set up. It will take more work but be worth it. You need to make sure the deck is prepped and true. Machine the cylinders and ONE piece head for O-rings like you see on the race cars. Maybe even give TDR a call for their one piece girdle head.
I did finally get mine to stay sealed up with a stock head machined head and a Special TDR Big Bore gasket with metallic compression rings in it. But if I ever touch those cylinders again I'm doing the metallic o rings