I took a look at how he did the tracks. A lot of flatbar drilled and welded together for links. I would just save hours and hours by buying some conveyor chain and using channel iron welded to them. The only thing is making sprocket to match the chain.
For a quicky fix to protect my tires in a thorn infested area I put tracks on my tractor. I built a track for each tire. It worked great and was easy to take off and on as needed. Tractor drove as normal. I have often thought of building a subframe for a small tractor. Having the rails and idlers on both ends, Would just be a matter of dropping the front axle off the tractor, and bolting the track frame to the tractor, replace the backtire for a sprocket and running the track up over it. Not unlike the highsprocket system of the caterpillar. A person could put a braking system using the pitman arm of the steering with two master cylinders apposing each other. Just an idea I have had rolling around in my head. Would be the primary turning system with differencial brakes of the tractor for help if needed.
By making a sprocket the size of the rim not the tire it would be an automatic gear down and easier on the drive system of the tractor to include the tractor brakes. As most newer tractor brakes are oil bathed, it would not be that hard on them. Also with the rear idler being just forward of the lift arms instead of straight down from the powered axle it would make for a longer system for floatation and make it less likely to rare in steep ground or heavy loads on the 3pt.
For summer it would just be a matter of breaking track, lifting it, replacing the front axle and putting tires back on. By breaking the track at the front idler and lying the track to the rear, the carriage could just be rolled to the rear to replace the wheels. For braking, would not be to hard to brake the idlers by bolting drums to sprocket/idlers