how to tub

Hi, I have a 74 Ranchero that I wanted to slap a pair of really wide M/Ts. I bought a pair of weld rims that have a backing space of 5 1/2 but it still sticks out by about 3/4 of an inch. I plan to have the 9" shortened but don't I need to tub it as well? Is this difficult to do? someone gave me a pair of tubs but all I can do is stare at them and wonder what the heck am I going to do!!!???
any assistance on the matter will be greatly appreciated. I also wanted to post pics of my cars and project but I tried several times and it won't let me. Guess I have to minimize or something and that's something way too techno for me. (guess I'll wait till my son gets the time to do it).

Rene'
tripod396@msn.com