Bob - you got it right. The D17 was 7.25:1 compression for the entire run from 1957 to 1967 for gas engines. The Gleaner E combine came out with the same 7.25:1 engine in 1962 somewhere in the middle of production it switched over to 8:1. 1968 EIII Gleaner was also 8:1. 170 was 8:1 and 175 8.25:1. The 175 also got a 1/8" bigger carb too. The G226 engines have codes in the serial number on the block behind the carb to tell you how it came from the factory. M=7.25:1, Z=8:1, V=8.25:1.
Right again that the D17 was 1650 rpm's and the 170 & 175 were 1800 rpms. The earlier WD45 with the 226 engine was 1400 rpms. When Allis first designed the larger 180 tractor it planned to use the 226 gas engine running at 2000 rpms. And yes they were concerned with vibration since it was not counterbalanced as you point out. The prototype met the specs and Allis built 100 of them with the 226 engine. The production versions had vibration problems when they tested them. They went back and retested the prototype and it it was fine...apparently a one of a kind anomaly. So Allis had to back to the drawing board for a few more months and decided to use the 265 6-cylinder gas from the 190 with a smaller carb for the 180 gas (I have one love it!).
Another note on the D17 226 engines...early ones up to SN24000 had a bypass oil filter system ...24001 & up used a full flow oil filter system. Another change I believe in the heads was going to 3/8 reach spark plugs plugs in early D17's to 3/4 reach plugs. But I can't find where that SN break is even in the parts book. Mike