Will a mtb brake lever(2-3 finger)fit onto my 26m track bar? I want to position it down low so you could only activate it while riding in the hooks/drops.

maybe i don't understand where you want to place it, but wouldn't an aero lever be a better choice?

it's useable from the drops, and if you position it low enough, even from the flats at the end of the drops (if that makes sense)

most importantly (aesthetically speaking) is that it will give you way cleaner cable routing, as you'll be able to run it under your wrap, assuming you wrap. if you don't, you could at least tape it down or something ... cleaner lines ...

that's my two cents, anyways ...

seems to me you would need very long fingers to activate a MTB brake lever in the drops, there are lots of used aero levers available, see above advice from SSSasky