So my 83 Brat (totally stock) is getting progressively harder to shift into 1st. What I mean is that the stick is physically hard to push into position and it feels like it pops into it. Sometimes it's almost impossible and I have to shift into R or 2nd before it will allow me to get the stick in 1st. I'm assuming it's some sort of linkage problem? Also on occasion it will pop out of 3rd or R if I accelerate quickly. It doesn't feel sloppy at all, just like it gets caught up trying to move into the right position. Clutch is great, no weird noises or engagement issues, just the stick. Any ideas?

The syncros in the transmission are wearing out. Mine is the same way; Common on these transmissions. There are some additives that help prolong the life, but you can drive it till it just won't go into gear anymore. After that, your options are to find another 4spd, do the 5spd, or Go EJ everything. There are also some other alternatives.