For anyone who happens to land here from google - HELLO FROM THE YEAR 2021!
Figured it out, at least I think I did. Went back with a fresh set of eyes this morning and realized I had the shifter linkage (tie-rod looking piece) swiveled around 180 at the end that attaches to the shifter spline on the bike. Pulled it off and re-installed it correctly and the shifter now works, albeit the lever itself is sloppy as all hell. Re-adjusted the clutch according to the LT160E manual's procedure, and it all feels right now. Going to test fit a few short throw dirtbike shift levers on it and see how they feel.
Hagbard's post in 1987 LT230E won't shift after misguided clutch adjustment. was marked as the answer