I did a few more calcs with closer numbers and it turns out that a standard bore 216 with a 235 crank, rods and Buick 215 pistons winds up with a compression ratio of 6.25:1, down from stock 216 6.6:1. That's because the Buick pistons land 1/8" below the deck of the block and have a recess in the center.
Probably not a huge thing in the big picture. If I go that route, I'll likely get the crank reground offset to 40 undersize on the crank pins which would increase the piston height by about 0.015 at TDC. Decking the block a bit would help as well.
Here's the numbers.
Compression height on 216 pistons, 2.0625”
Compression height on Buick 215 pistons 1.843
0.2195 shorter
Add back increase of half stroke difference +.094
puts piston crown ~0.125 below deck.
Stock 216compression ratio 6.6 to 1
Stock 216 Stroke volume per cylinder 36.08 cubic inches.
Compression volume V
6.6= 36.08+V V=36.08/6.6 = 5.46 cubic inches.
Add 3.5^2*0.125*pi/4 plus dish volume in Buick pistons (2.812^2*pi*0.15/4) = 1.20 ci + 0.56 ci
New compression volume =7.22 cI
New stroke volume. 3.5^2*3.938*pi/4 = 37.89 cubic inches.
New compression ratio (37.89+7.22)/7.22 = 6.25
