Lengths of old steel plate will work, too, if you can source some. You can also use wooden railroad ties, this has the advantage of raising the tractor up, and make it easier to slide underneath when you have work to do on the underside.
The downside then, is it makes it harder to climb up on the tractor! A set of steps is always useful in a shop, anyway, for climbing up and down - they generally save skin from being scraped!
When I built my shop in 1975, I installed 6 lengths of rail line, in two sets of 3, about 10" apart in the floor, with the head of the lines just slightly above floor level.
That floor endured multiple D7's running in and out on it, for many years, heaps of track rebuilding, tractors screwing back and forth - and the floor is still good today (I sold the property and shop to a friend in the early 1990's, and moved away, but I've been back there occasionally, over the years).