Buy the tire / caster swivels from Harbor Freight and ask your friend to cobble the rest up from scrap material if he can. Bolt up to the bumper bracket holes in the frame.
Wow! Your garage looks great! I have to admit thought, I was having a tough time not starring at your 'cuda. Sweet ride for sure. I spied 2 trophy's in the reflection of your workbench... nice image!
Back in the early 80's, I lived in a mobile home. I bought a Morgan Building garage to work on my Duster. What's interesting is I got a lot more done in that little garage than the one I'm in now. :banghead:
Thirty bucks, Harbor Freight and a few beers, netted me a set of homemade front end casters.
Notice that the slip tube is rather long just in case I needed to raise the car up. I didn't need to, but it didn't hurt anything either.