I would buy replacement feet w/ t nuts and make them work properly! just my $0.02
TFT
I like this idea, but it can be a bit costly.. On the other hand, if you can find someone to machine the components, it's not horrible.
I made these a few years back:
You can also drill and tap the feet, and buy some 3/4-16 threaded rod and jam nuts. It's still not all that cheap, but it is cheaper than buying a replacement set.
Alternatively, you can drill and tap the current feet, and use a smaller thread, with a more common size T-nut. However, it won't have the strength of the 3/4".
I might recommend:
1/2" T-Nut
1/2-13 x 3" Threaded Rod
1/2-13 Black Oxide Nuts