Hello Mark. Nice to hear you have a 1931 model 57. I have a 1931 model 54 and did a lot of mechanic work on it. (if you want to have an impression: look at the memberscars on the BCA-site). Indeed, as you have experienced, you can remove the piston and rod from the bottomside. And I understand you don't want to remove the head, because it's a lot of work. But I have to disappoint you: it is impossible to assemble it from the bottomside without damaging the rings. There is no way to compress the rings with a bushing or so because the space is too tight to slide such a bushing back along the rod. Using your fingers is not a great idea too. So I think you need to remove the head. Please let us know your experience on this. I am still learning. Best regards and good luck. Alex Veen, lexveen@hetnet.nl