I just found the tag on my rear axle of my '52 F1. The VIN plate says 4.27 but the tag on the axle says 47/12. That equates to 3.91.
I thought all pickups had a very low ratio rear end like the 4.27 the VIN plate indicates.

Will the 3.91 work allright for a 235 flathead and light duty three speed?
Don't want to install a later model 9" diff if I don't have to.

 

the 3.91 gears will work fine if you want to run 45-50 MPH, but if you want to keep up with traffic, you'll need to get into the 3:00-3:25 range.

 

Here's the rear end specs for the 51/52:



So it looks like your calculations are correct. Have you bounced the Serial Number on the Glove Box Rating Plate off the one stamped in the frame (passenger side just aft of the shock mount)?

It's possible you have a different glove box door, or just as likely it's not the original cab for the frame (or someone didn't like the low gearing in the original rear end and put the higher one in) (or, or , or)

If you want to stay stock, the 3.92 is as high as you can get and it should take you up to 50 (downhill, at 3000 rpm, wind at your back, with 1/2 ton of sand in the back)

 

Thanks Julie and Jeff. The frame number is different than the glove box door. The glove box plate is attached with screws so I won't take that to the bank. this truck is a mismatch of colors so it is probably made up of donor vehicles. I bought it from a guy in Colorado who had a few trucks in his garage in various states of repair.

 

Bingo!!!!!!!