I have the chance to go pick up a free 1971 310 with a bad BGB this week, its a super clean but well used machine owned by a buddy's dad. It runs and drives fine but I had checked the BGB last year when I was there and it had about 1/4 turn of play in it. It makes no noise and the shafts feel tight but there's a ton of backlash.
Its done nothing but mow grass since new.
I'm heading that way for the holidays this year so pretty much either way the 310 will be heading back with me. What it needs will determine whether its a keeper or parts machine I guess. The best part is that he replaced the motor several years back with a rebuilt K341 16hp which still runs like new.
Either way, the price is right.
I've got a few good used gear boxes here, will any of these fit a 310 with variable speed gears?
I've got one from a 3415H, one from a 410 3 speed, and one from a 7016 3 speed. I may still have one from an older 3112 too but I've yet to put my hands on it. It may have gotten used or traded off.