342 ?

The 4th bearing will protect the crank from breakage. The J/S will allow you to keep the extra heat from the clutch going back into the engine, and also running like a 2:1 primary ratio will lower the clutch engagement which will keep the clutch cooler and make it last longer. Also if your engine has a 1'' crank journal you get the belt driver for a 1'' and then you can run the regular 3/4'' clutch on the j/s. Yes it is extra expense to start but the idea is to save you money in the long run and make your equipment more reliable. Burris makes a nice 4 stroke j/s mount that I would look into.jmo
when we was running our 342 short block we were using a mini drag bike head that was built with a 38mm mikuni. we had to go back to a 305 short block and runs just as good as before
we needed to deck the block after blowing a headgasket and didnt have time to do it being we was at a race, so we reblocked it in less than an hr