I suspect the "+.020" deck height spec was more for the NHRA than what the actual deck clearance was.
Seems like the tallest replacement piston I remember seeing for one of those has a 1.920 CD.

I think many of the rebuilder type pistons are more like the 1.848 CD variety, and some of those have a dish in them to boot.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads