The only Baker Hill to 4 chain adaption that I know of is my modified, and that's a 6000 with no reverse. That machine is a Rupp 440 liquid cooled and started out about 75 hp- not sure what it is now. It's not an easy job- lots of fab work. You may be better off using a T20 and leaving the BH for a first gen machine. The 7000 reverse unit tends to pop out of gear after it gets lots of hours on it, so there's that to consider as well. Parts are getting hard to find: I have some but not a lot, Richard's may have some left and I know MudOx had a couple first gen machines with the 6000 trans for sale a while ago but they are probably gone now.
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far