you should be able to go to the local Chevy dealer and give him the infomation off of the data tag on the rearend of the bus. If not go to a "big" truck dealer. I know that sounds easy but I know how finding the correct info can be sometimes. Also that is a "tall deck" engine if memeory serves me correct. If top speed is a concern then you will need to swap rearend gears to change speed. I believe those type of engines are like diesel engines,,in that if you want higher top speed in high gear then a gear swap is the best way to go. You can "turn-up the fuel" on a diesel,but if done too much it will be turning too many rpms and eventually "break". A gas engine can be made to run faster but then fuel mileage is a concern then. Good luck....
freedoms just another word for nothing left to lose