you could swap a 54-60? pumpkin in your axle, and still use your brakes/parking brake, etc. the gear ratio will be 3.90. you could get a set of 3.38 gears and have them installed. Obviously you would have to weld on new spring perches to your axle and get rid of the pivot mounts associated with the torque tube. With the pumpkin swap, you are left with only 2 gear ratios to chose from. You are also left with 55 year old drivetrain parts with 55 years of wear.
Another option is to find another suitable axle. They aren't as hard to find as you think. The 4wd chevy and gm trucks used a narrow 6 lug axle for quite a number of years. For my 1940 I also wanted a 6 lug rear, and disc brakes. I ordered an IMCA modified F@rd 9 inch rear. I was able to spec out the 6 lug on 5.5 inch lug pattern, width of the rear end, number of splines, size of the disc brakes and more. The 9 inch has virtually an unlimited number of parts and gears and positractions to chose from. Best of all you can get all the parts clean, new, and from your computer without having to drive around to all the wrecking yards to crawl under 100s of cars and trucks with a tape measure only to find a warn out oil leaking pos axle that the wrecking yard will let you have for 4 bills. After cleaning and rebuilding you could be out some serious money.
