Can be done if you use diesel "M" skid_pto_radiator and hyd pump drive sheave. The 350 has complete different skid, pto housing, radiator, and the hyd pump is driven via countershaft. The wiring to the 301 should use most of same harness with the coil wire going to the fuel pump shut off. The gas harness will not have an air heater wire. Throttle cable should work if you route under water pump to fuel pump.
No comparison, but I recently switched engines on a couple of K2s(gas to diesel). loosed 4 bolts, wiring harness, and throttle cables and lifted engine, radiator and hyd. pump from one to the other. Had to also switch drive belt and unloading belt. I took 2 machine and built one good one.