For antique tractor pulling, you want about as little psi in the tires as possible. 10-20. Think of it like this, when you've got low psi's, the tire is running flat on the bottom. That flat tire then begins to look more like "tank tracks" than a round tire. Too bad you don't have an agressive tread, that'll do more than anything.
Course antique tractors don't ever spin out, they just lose traction. 4-5 mph speed limit.
If you don't have a speed limit, get it going as fast as you can as early as you can. If you can add weights (is it a weight class restriction) sounds like you would want to add some weights behind the rear axle as far as possible.
Have a good time, make a lot of black smoke. The crowd will love to hear the sound of that screamin jimmy... not really a jimmy but close enough.
