[Mike Taylor 3601]

267,305,350 all are same crank, EXCEPT for balance,you can identify them by comparing counterweights,267 will have deepest holes,305 a little less, some 267/305 cranks have notches cut in counterweights to remove weight.

I would at least try to find 305 crank, or balance the 350 crank,I balance everything,be surprised how good a 3.5 briggs will cut grass when balanced,took 2- 3/4X3/4 pieces of heavy metal.
Might get someone to balance w/bobweight made up from 1 piston/rod.

Mike Taylor 3601