Brian,
Per 464me: ditto - not sure that 46 the 3/4 tons are the same as the 1/2 ton but I used a 55 pumpkin in my 46 1/2 ton. I too understand any year truck 1/2 10 bolt punkin from 55-62 will work. Most of them will be a 3.90.". Work meaning your axles will match the spider gears just a punkin swap.
I too agree with Big - gearing between a 3:90 and 4:10 is not much difference. That was why I opted for a t-5 with OD. The gear ratio and tire height did not "give enough" for a 70mph, 235, @ optimum rpm. If interested my 46 swap is documented in picts on the fliker link below.
Cavebull
