Hard downshift from 2nd gear to first. A-833 4-speed.

Yeah, Ima thinking technique.
Here's something you can try .
drive the car in first gear, up to a speed that makes 2500 rpm on the tach , look at the speedometer and make a mental note of the speed. I'm just guessing but say it 20 mph. Now, you will forever know that for zero speed difference of the input and output shafts that 20 mph (or whatever it is in your car) is 2500rpm. So then you know that to downshift into first at 20 mph, the rpm will need to be around 2500, to rule out problems with clutch departure. So go out and practice it.
In second gear at say 22 mph, press the clutch pedal down, bring the engine to 2500 rpm, then wait for the car to slow to 20, then ram that stick right into First. See how easy that was!
Oh yeah, about declutching ; how far do you have to press the pedal? That's easy to figure out.
Start the engine, push the clutch down, put it into fourth, then while slowly bringing the pedal up, watching the tach. as soon as you see the tach dropping, or feel the car moving. that is already not enough pedal for to shift at, so press it back down a bit, and make a mental note of where the pedal is, relative to the floor.
Now, adjust your seat to make that position, the default position, with your leg comfortable enough to hold it there. Now try again, this position needs to feel natural. If your leg is uncomfortably bent to limit your leg power, this will not be natural. If your seat is too high this is gonna be a problem. I put the ball of my foot on the pedal and slam it down until my heel touches the carpet and so, I have a repeatable declutched position that I never have to concentrate on. I re-engineered my seat tracks so that this occurs with my seat all the way to the front. And I changed out my steering wheel until I found the perfect combination of dish and diameter, so that this is comfortable for like 90% of the time. On long trips I move the seat back some more. Thus all my muscles have memorized the constant seat position, and so the clutch is always pushed down to the same position.
Now, after finding that position, with the car stopped and engine idling, push down the clutch and attempt to engage reverse. I bet it grinds, Wait 5 seconds and try again, if it still grinds, wait 5 more, and try one last time. Then rest your leg.
It grinds because the cluster is still spinning, and there are only two reasons for that;
1) the clutch is dragging for lack of departure, or
2) the clutch is dragging for lack of the pedal being pushed down far enough.
3) at most, I might expect the gears to have stopped spinning by 5 seconds.

Therefore repeat the test but this time depress the pedal another inch, and wait 5 seconds, then try it. If it still grinds, I would bet money that the disc is not coming to a stop. To engage reverse, with the vehicle not moving, the disc has to stop! So if you get into this situation, figure out why the disc won't stop, and fix it.
Here are some of the reasons; in order that I would suspect;
1) insufficient departure
2) a bent disc. that is to say, disc not perpendicular to the hub. This only happens if during installation the trans was hung in the crank before the retainer was fully inside the bellhouse. The only cure I know of is to replace it.
3) a warped disc, which is to say cupped. You measure the departure as ok but towards the center, the disc is dragging. Gotta replace it.
4) clutch fingers not all adjusted to the same height. . You measure the departure in one spot and it's fine. then you find out, it is less/more in a second spot and worse in another. Only cure is to take it to a clutch shop and have it readjusted.
5) packed up organic linings.
6) BH severely out of alignment with the crank and/or flywheel. Ok so bedtime for this cowboy.