Wow, That's a beautiful truck! I'm sure your family is very proud of your accomplishment. I put a sterling 10 1/4" axle under my 59 F350. It's a 4:11 and with my little 223 six, I can't really start off in second, ok maybe downhill. I can however go 70. The axle came from a 92 f350 dually pickup and we can assume that did 70 quite well. So to give my .02, I would say with your 292 that the 4:11 ratio would be a good choice if you still want to haul heavy stuff on that flatbed. Tire diameter affects things too and I had a formula in a book once that gave rpm @60 mph. It takes things like tire dia x 3.14 x axle ratio divided by 5280 or something , anyways I was terribly bored with math as a kid so am challenged by it at 58. I'm sure someone can direct you to a site that has it. You will then know what your rpms will be at 60 mph. Good luck and welcome to the fridge community.