RE: fpe 5.8 with the shakes...
A lot of motorcycle engines have used and continue to use solid mounts. I've owned a few big single cylinder ones that didn't have balance shafts...580cc Triumph MX, and Yamaha 540cc Enduro. Both of them started as 500cc engines that wound up with big bore piston kits. No bearing problems. I believe the harmonic balancer on the crankshaft of a V8 or straight 6 serves to keep the crank from failing from the twisting vibration you find in a long crankshaft. Short stout cranks like we have in model engines and motorcycles don't need a harmonic balancer on the crankshaft. Flexible crankshafts cause the problems.