I made those for my bandsaw, Bob has plans for those if you've got some 40, 50, and 60mm box iron, I had only thin wall box, so I added a bit more flat on the underside of the 40mm lever, and welded a lip to make the end blunter, as I cut the toe of my boot with these before.
http://www.thewoodhaven2.co.uk/viewtopic.php?f=23&t=216&p=1295&hilit=wheels#p1295
Look up Carl Holmgren on YT, and be inspired
It's a much much much nicer solution, and I guess would work well with a P/T
as the weight would be even on both ends, and no obstructions to account for.
Not going to lie, took a few lessons to find out, these work best like that,
and should one be wanting the casters concealed, it might be best to do a mock up first,
to check if the machine might dip, when the caster swings over.