hello new to mopar slant

Guatemala? Wow! How many miles (km?) Are on that thing.

I have a /6 3-on-the-tree in a 1964. Just over 100,000 miles. There is an adjustment shown in the Factory Service Manuals that may help out. Not just center-to-center rod length, but rotating a sleeve to take up slack. I've done that a couple times but started to have problems again, just as you describe. If you need new rubber bushings for the shifter rods, I have some. That also helps. Honestly, I don't think Brewers can help much. You also have to assure enough clutch disc departure.

You most likely have the baby trans like me, "A903" non-synchro first and reverse gears. Unfortunately, there are no provisions on the case to mount a floor shifter. A shifter mounted to the floor with rods going to the trans introduces another place to flex and bind up. If you can find a newer 1970-1981 all-synchro "A230" to swap in, that's a good way to go. I believe that's the one that had a floor shift standard. (Dusters, Darts, etc)