Assuming that the transmission and rear end are original it is either 4:11 or 4:56. Can't remember what the 3/4 tons had. If it's 4:11 you can run it 60-65 w/o hurting it. I've run mine over 75 and it's still together. Don't worry about the noise it makes running fast if it's in good condition. They sound worse than they are. A 4:56 may be a little too much for anything over 55. Remember you stil have the old 45-50 mph brakes so don't get carried away with speed until you've addressed the rest of the issues.

1953 Chevy 5-window 3100
In the Stovebolt Gallery
More pix on Picturetrail

Dave
Engine & Driveline Moderator

If you can't make seventy by an easy road, don't go. ~~ Mark Twain