Anniversary rails won't have floating nut plates. Those weren't introduced until '64 or so. Anniversaries will have the figure 8 nut plates. If they aren't failing and you don't have the tools or skill to fill in the void with wood and replace with threaded inserts, leave them be. If you [lan to replace the cushions, the subrails don't need to be replaced (unless they are stapled out), but the bevel does need to be adjusted so the table remains a 2:1 playing surface with new cushions. Modern K55 cushions are 1/8" larger than the Monarch SuperSpeed cushions (profile no loner available) so if you install modern K55 on your Anniversary rails w/o adjust the bevel, you'll wind up with a playing surface of 49.75"x 99.75", not 50" x 100". Also, if you are not paying attention to nose height when installing on non adjusted subrails, you could wing up installing the cushions too high or low.
I'm not sure you could install adjustable feet and I'm not sure I'd use t-nuts to fasten the slate.
