My '54 GMC 2 ton,in low in both boxes and the axle,is good for 1/2 mph at redline. ;)But,yeah-you have the SM420;I like that box a LOT better than the 435 or 465,but around here you have to fight the off-roaders for 'em.
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck