Not sure what you mean by your last question:  There are at least 3 different 88 blocks and there are changes in the last one with no casting number changes. For the 770 there were 3 blocks one of which is the same as a 1550 but none are the same as a 77. You did not answer my question on the 1650 as the gas have 4 main bearings and there are 2 of those plus the diesel are 7 main bearing blocks and there are at least 2 of those.