The biggest that Kohler currently makes is a 40 Hp carb. model it weighs in at 132lbs dry. The 35 b&s weigh 135 w/muffler. Kawasaki is producing a 37 hp but the biggest crankshaft they offer is a 1 1/8"
The boys at Gator Trax have a modified 35 at 45 HP. There are 35 BS out there in use on mud motors that are at 50 hp and above it all depends on how much money you wanna spend on engine work.