I have been meaning to do this since I built the tractor, it works great but due to the weight and the live rear axle it is a bit dangerous on hills. got a donor bike given to me for the rear wheels and the free wheel gear. pics give the details. when I built the rear axle I made a place to put the original band brake on there, I modified the original attachment lift handle, and made a different adjustment plate with teeth rather than holes, added the bracket on the bottom and re attached it to the tractor, After putting the band brake on I went searching thru the parts pile and found an old mule drive assy, removed the spring tensioner and made a new rod to attach to the band brake, Viola. brakes that work.
Worked out even better than I thought it would, tomorrow I am going to work on changing the front tires over to the new ones, I found a set of plastic tires on a big wheel push mower that are the rite size, than after that I am going to put the free wheel gear on the pedal axle and the 20" bmx tires on the rear. ought to look good when it is done. I only wish I could have found a set of plastic bmx wheel to match the fronts. I will post more pics as I get thing done.