The forward half of the 319 is identical to a 318 except for a hole for the reverse lockout. It shouldn't be any problem to put the B-W OD on a serviceable SM318.
Lots of good info on the OD
here. I recently replaced some gears and the bearings and seals in one for my '54 GMC Suburban. I love it. Drove it from here to Phoenix last month and it was nice on the highway.