My two cents, I have noticed that replacement pistons tend to sit lower in the hole for decking cleaning purposes. One can still maintain a compression ratio and still get a flat clean surface to bolt a cylinder head to after decking.
Your right Curt, I just measured the deck on my new 261 short block and couldn't believe there was .060 there, and that was after .010 was milled off the block before assembly. This got me thinking of what my compression ratio was going to look like, so I ran some numbers.Sorry to load it into your thread but it kind of goes with it all.
Swept piston area within the cylinder: 235 (.030 over)= 654cc (A)
...........................................................261 (.030 over)= 724cc (A)
Cylinder head 850.........................................................= 86cc (B)
......................848.........................................................= 79cc (B)
compressed head gasket thickness (.042)...................= 9cc (C)
Deck (.060) 235...........................................................= 10cc (D)
....................261...........................................................= 11cc (D)

CR= A+B+C+D/B+C+D

235 with 848 head= 7.7
235 with 850 head= 7.3
261 with 848 head= 8.3
261 with 850 head= 7.8
if you mill the head, add .12 cr for every .010 taken(milled off the head surface)
These are my own calculations but feel they are close, use at your own risk.

Last edited by sstock; 07/02/2019 2:11 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration