833 OD sticking in 4th, chipped synchro

Yeah what He said^^; and thanks to @446acuda, for that update.

Now, to the OP, Thanks for the new picture, which shows that the mainshaft appears to be in the correct position. So then, If the slider was in the position shown, with the cover installed, then it most definitely is over-shifted. With the late style cover with the scissor interlock, this is not supposed to be possible.
So then, what I would do is;
Firstly; examine the 3-4 fork, and make sure that it is not bent. The centerline of the pin should be on the same centerline as the fork-arms. If you are able to, put the pads of the forks onto some kind of surface and make sure the pads are parallel, and that they fully contact your test surface, simultaneously. If the fork is bent, it will usually show up as pads that are worn unevenly. Obviously, if the fork is bent, throw it away.
> But if the fork passes;
>Level the box front to back, cover side up.
>Work the struts back into the slider and put both of the sliders into Neutral. You may notice that in Neutral, the 3-4 slider may move back and forth a lil. see Note-1
>Pull the 1-2 fork out of the box. Install only the 3-4 fork.
>Install the cover with the two extra-long-shouldered bolts in the correct locations, finger tight.
>Shift the box into direct, and spin her over a few revolutions; then remove the aligning bolts and lift the cover straight up, fork and all.
> if the slider did stay where it's supposed to be, lets get a pic of where it is . If it is in the correct location, then we gotta figure out how it ended up being over-shifted.

Note-1
The struts are supposed to pop up into channels in the slider, and minimize that, but the fork will center it. If the strut springs are too slack, you can only change that after a teardown. I stretch the crap out of mine before I install them.Because, it is the dtruts that push the brass onto the brake cones to slow them down, and they only have a few milliseconds to do it during the typical shift. If the slider moves over them too fast, the clutch teeth will clash and tear off the points. Eventually, shifting becomes difficlult as the teeth brass stops working. Look at the teeth on your overdrive gear; they have already been butting for a long time. The point is this; stretching the energizer sprinds will make the shift effort slightly higher. But your struts will finally be able to their job. Just stretch them!.
BTW, if you are running a synthetic trans fluid, good luck with that. Thatstuff is so slippery, it takes forever for the brass to reach synchronization. Couple that with weak energizer springs and gear clash is the natural result. I run 50/50 DextronII and 85/90EP oil. The EP oil helps protect the cluster pin, and that's the only reason I run any at all.