The wheels you have on your cast spokes are called "Dayton Wheels". The spokes can accept both 20" tube type split rims or the 22.5" tubeless one piece rims.
The 6.17: 1 rear gears were the fastest gears available and you should be able to run about 60-65 mph all day long. My 1957 Fire Engine has 6.14 gears and that's what I run on the interstate. It takes about 1 mile to get there but once there it runs fine. My truck had 11K miles when I got it and it now has over 41k. Don't be afraid to bump the governor once in a while, the engines are made to run wide open all day long.
Get the truck running and drive it for a while before your tear it apart to make it go faster, you might be happy with the speeds you get as it is...
Mike B
