making car mobile without a k-member

Probably go with something along the lines of donnielwasons, cause my trailer wouldn't be long enough with it mounted at the bumper. What type of caster did you use, I looked at a couple places this weekend and saw rubber wheels(kind of a fraid they would develop a flat spot), polyeurathane wheels, plastic and steel. Thinking of 8" to make it easier (hopefully) to load on the trailer. Will have to scrounge around our junk pile or go to a steel supplier for the materials because we can only get steel for home projects at work on the last friday of the month and it now has to be approved by 2 people. Any idea of what the wieght on the front would be? 67 Dart convertible, full interior, no engine, trans(obviuosly), no front bumper.
Thanks