Final Results:
I am very pleased with the result of my hard work. I was relieved to find that the weld in the cove and tread bay radii blends smoothly and seamlessly with the rest of the treadbox.

Raising the Top Wheels
This is a project was a mess. I raised the top wheels a quarter of an inch measured from the outside perimeter of the countersinking hole of the existing hole to the counterskinking hole of the hole I wanted drilled. This seemed right to me. I determined that this was the correct distance by placing a wheel in the upper bay with the tread on top and seeing how high I could raise it without letting the tread touch the top of the bay.

I then had all eight holes cut using these measurements. The outer hole of each bay had to be countersunk and the inner hole had to be tapped.

Unfortunately, I only measured the outside bay. I failed to notice that the roof of the inner bay was substantially lower than the roof of the outer bay. Consequently, when I tried to install the wheels and treads, there was no room for the tread in the inner bays. My heart sank.

I remeasured and found that the correct increase in height was exactly midway between the old holes and the new holes. I had to have all eight of the new holes and all eight of the old holes filled up with weld. Then, eight new holes had to be drilled, countersunk, and tapped.

No one will ever see my mistake because the weld filling in the holes is sanded perfectly smooth to blend in with the surrounding aluminum. Also, the wheels hide the injured areas. Still, it was a very silly and expensive mistake to have made.

---