My understanding is that clutch gears with shorter splines are OEM and the ones with the full splines were aftermarket. In which case the aftermarket parts would be presumably stronger. I don't have any evidence to support this claim however.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine