ok I'll give you 2 66's , a 15-91 and a 6 pack for the 61w. recently I have gotten a 61w156, then for parts a 61w52
only difference I can see is there long bed and short bed industrail version 's. There porn to hook and bobbin case wear and a link rod that works the take up arm breaking, Today I just found out , there are aftermarket parts for almost all singer industrails