I also don't understand how with 72 cc #17 heads you only have 8 to 1 compression and with higher volume 87 cc #64's and no other machining you mentioned...you are at 9.1 to 1.

With larger combustion chambers as the 64's have...you LOSE compression. Somehow your #17 350 heads are 8 to 1 on your block when according to math...the answer is 9.9 to 1. And the same math you came up with..the 64's (absent any info provided) they are magically 9.1 to 1...when math shows they are 8.6 to 1.

Some sourced place your #17 heads at 72 cc...some say 80 cc. With 72 cc, they are 9.94 to 1 compression. With 80 cc...9.22 to 1. Now...taking into account the only differences in the parameters that affect anything is the chambers and valve size...you have larger valves with the 64s. In order to get the 9.5 to 1...you would need to mill a minimum of 7 cc's from the heads or block or a combination of both to achieve a 9.1 to 1 cr. Another 3 cc's would need to be milled to achieve 9.5 to 1.

My consensus is...if you bolt those heads onto the block with no other machine work, you will be at 8.6 to 1. Although your 17 heads have 9.2 compression now...yet smaller valves..putting the 64s on is a wash. Yes you have larger valves...but NOT the compression...so i surmise your new dyno run will fall flat on its face.

I guess i am stymied by how you got your numbers.