I blew up a SM420, about when I was 17 in my '65 3/4ton with 4.10 gears and the stock torquey 292, but I haven't had any problems with the SM465 in my 85 K10, but then again its only got a 305.
I dont like the overdrive on the 700r4 in my 82 suburban, its kind of annoying how it shifts, but then again I've been a manaul tranny guy and I've only been through one clutch in my 85.... Do you need a different clutch from a small block to a big block?