A518 with No First Gear (so it seems)

Hey guys, just trying to get this figured out. I did try searching but came up with lackluster answers so I'm hoping I can get some insight into some good troubleshooting tips.

I have a 74 Duster that came with an A518. Cars been sitting for a while now, finally got around to firing it up but I remembered that when I put it away it had troubles with first gear.

Just took it for a spin and confirmed that it doesn't have first, even when I manually shift it into first. It has everything else like 2/3/N/R/P (2/3 as far as I can tell) but I didn't get it up to any kind of road speed just in case something cratered.

Fluid is good, and based on what I found it could be linkage, governor, etc. Any help here? I'm hopeful that since I still have reverse that this thing isn't pooched but I'm pretty new to transmission tech so who knows.

TIA.