HELP 3 rail curves and switches

This answer is probably headed in a direction different from what you are asking. Whatever minimum curve you are running has no bearing on the switch size. You easily can run 072 switches with your 060 curves with no issues.

Back to what I surmise is the core of your question. If you have engines/rolling stock with a stated 054 minimum, you would be well served to not use switches tighter than 054 (say 042 for example). Minimum radii have more to do with switches than curves.

Not really. A lot of people want minimum curves of O72 or more, but have equipment that will run on smaller curves. They just think engines, in particular, look better on wider curves and there will be fewer problems. If your equipment will run on O54 curves there’s no technical reason not to use them if you need to and they fit the design.

The angle vs diameter/radius are different things.

Lionel uses R/Dia turnout exits, not a number and deviation angle like real RRs(the real turnouts use # /angle, not actually a curved exit.

You can mix larger than minimum, sure. But geometry gets harder. I.e. if you want all FT to line up perfect you are going to have to really plan hard, and may fail; need custom cuts, etc. (Same with tube track, but cutting is straight fwd. and easy.)

Flex track made this all so easy, then the snap together roadbed track made it even harder.