Hello  Looking for source of parts. You probably have guessed cluster and low gear. I rebuild trans (new bearing and counter shaft)  30 years ago and put in a used gears (cluster and low). Trans howls in low gear, I suspect  I used a missed matched set, they looked just like original but there are no part numbers on gears. I haven't driven car much because of this but decided try to fix it (third time).  Have trans on bench, built a fixture to spin. The noise is coming from cluster and low. I didn't notice noise as much in reverse, everthing else worked fine. I know BW had different gear ratios but thought tooth count would be different.  Not going to put it back in (56 TB) until it is quite on bench. Would like to fix if I can find parts but I have a tin top 4speed if I can't. Sorry for long message.  I have reached out Mike M, Vanpelts, TB vendors. Thanks Bill  Oregon