I'm tryin to see how feasible it will be to modify an input drum to accept TH400 direct clutches.
From my Alto book, it shows that the 80E clutch is 0.151" larger in OD than the 60E one. ~5/32" only. From the pictures I've seen of built input drums it looks like there is enough room to machine out the drum slightly for this larger clutch.
5.893 - clutch; 4.575 - steel. 80E
5.742 - clutch; 4.995 - steel. 60E