The 1975 K&B .35 is an engine I've never had, but I've had two K&B Series 61 .35's and various K&B .40 front intakes. My experience with them wasn't good, and the crankshaft was the main problem. Not sure if the 1975 .35 would have had the 'stuffer' type crankshaft, but some folks had the ring come adrift on them and cause havoc.
Mine usually snapped the crank off behind the front bearing (these were the ones with the prop driver held on with a set screw and later also pinned to the crank), but a few times the pressed-in crankpin came out and gouged into the backplate. The last type of K&B .40 (#4055) appeared to have fixed all that, but is about an ounce heavier. By memory, about 10.5 oz, which is just too much, and less stunt power than a .46LA. The best thing about the K&B #4055 is that the mounting bolt pattern is the same as a .46LA.
Steve