What I did for the casters was ordered two fixed 10" wheel casters and two swivel 10" casters from Harbor Freight Tools. Heres the link:
Fixed:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38943Swivel:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=38944I welded a 5 x 5 inch plate of about 1/4 thick steel to the tops of these. Then I took 4x4 inch by 1/8" thick square steel tubing to use as the stands. To attach the casters to the front I used the K frame bolt holes that are in the frame. I took the tubing and lined it up with the holes, marked where they would be then cut diagonally to form a prism type look. Then I drilled two holes in the tubing to allow for the k frame bolts to go through. I repeated the same process for the other side and bolted the tubing in to make sure everything was good. I then took another piece and put it up against the bolted tubing to form a perpendicular piece for the wheels to weld too.
In the back all I did was took a piece of the tubing and stood it straight up then cut away an opening so that it could be bolted to where the leaf spring hangers go. I marked the holes, drilled them, then welded the tubing to the wheels.
Overall it was pretty easy, the tubing could be a lot smaller but i chose to go pretty big just to be safe. If you need any help or if you want me to create a replica I could try. Heres some pics of the finished result.