Straight cut are aftermarket and are 100% the only way to use a drawn cup roller bearing instead of a bushing. It just never gets tight enough with the standard gear/bell. Reverse cut gears were made for 3 bearing engines, since they load the main gear outwards they don’t need the inner bearing on the main gear. Supposedly the 3 bearing case crank bearings last longer, but idk about that. Pretty much any of the homoet/simo high rpm piped puchs usually roast the crank bearings in a few thousand miles. Too bad even “quality” brands like skf and fag are made in Taiwan and China now.