1966 Valiant slant six standard transmission issue.

Having another mystery to solve on my 1966 Valiant 2 door post I just purchased from California. It's a three on the tree and after I got it running after many years of sitting I pushed in the clutch and went trough the gears. Its got reverse, 2nd and 3rd gear but when I try to put it in 1st it either goes in but it don't feel like its all the way in gear. If I try to go, it pops out of gear. If I put it back up in reverse and then try 1st again it grinds lightly, push it back up then it goes in but not enough to hold it in gear when I try to go. Anyone know what to try first? I'm really hoping it could be a linkage issue. Also does anyone know what transmission it is? Not sure, I just got the car a few weeks ago. Thanks in advance!