1964 a833 hard to get into first gear

When you are stopped ;
The driveshaft is not turning, so the trans mainshaft is not turning, so the synchronizer assemblies are not turning, but;
With your foot off the clutch, and the engine idling, ALL the other parts are spinning. There is no way under this circumstance to engage any gear; the brass rings would have to drag the engine down to ZERO rpm; that ain't gonna happen.
So, to select a gear, any gear, you have to step on the clutch, so as to disengage the running engine from the input gear. When you do this and all the stuff is working, the oil viscosity will drag the spinning parts down to near zero rpm, and then the brass can do it's job the rest of the way, and the slider can then couple the two parts together.
Occasionally, the brass works really well and sticks to the brake-cone surface, and the slider teeth may end up offset from the clutching teeth by a half a tooth, and then the slider bangs onto the clutch teeth and engagement does not occur. When this happens, you let the pedal up, the parts start spinning again, then pedal down the parts slow down again, and this time you don't wait for the gears to stop spinning, before you snick it into gear. That is one scenario.
Another is;
Occasionally, especially with thin viscosity oil, and a slightly dragging clutch, the guts refuse to stop spinning. There is no way, at zero mph, that the brass ring can synchronize the spinning parts when this is going on, no matter how well it actually works under other circustances.
Another is;
Occasionally, the strut springs are too weak, and the slider starts forward prematurely, and the result is grinding.
Occasionally, a brass-ring is not round, and bites the brake-cone in only two spots, so synchronization does not want to occur, so you increase pressure on the stick, the strut springs are over-powered and same as above, grinding occurs.
Occasionally, it has happened that a particular transmission does not like a particular oil, especially synthetics. Sometimes they are just too slippery for the brass to work the brakes; and/or the viscosity is too thin to drag the spinning parts to near-zero rpm.
Somebody rightly said that reverse is the acid-test for a dragging clutch; If/when the system is working correctly, you can select reverse nearly as soon as you have stepped on the clutch, with little or no drama. But if the guts won't stop spinning, it will grind every time and no matter how long you wait.
All these situations are for a stopped car at zero mph with the engine at idle.
Occasionally the engine idle is just too high. A833s are less sensitive to this cuz the guts are friggin' heavy, and don't want to be spinning in the first place.

If your trans guts are spinning for lack of departure, you need to fix this for another reason, namely;
Whenever your clutch pedal is on the floor; the TO bearing is pushing on the clutch fingers which is pushing on the clutch-frame, on the pressure plate, on the flywheel, on the crank, and on the Crank's Thrust bearing. The Mopar T-bearing surface is fairly robust, but you are putting a lotta strain on the system, in such a predicament.
If you have a dragging clutch, here are some reasons why, in order of most to least likely;
Lack of adequate departure,
a disc that is; warped, bent, fractured, or has a broken hub,
Clutch fingers not all set to same height,
crank centerline Not same as trans centerline,
Trans face Not parallel to Block rear face
Pilot bearing dragging,
Input gear dragging in back of crank,
Mainshaft seizing in back of input gear.

as for lack of departure, here are some reasons for that;
improper freeplay adjustment,
wrong pedal-ratio,
Wrong Z-bar
Incorrect working angles; The Z-bar should be parallel to the ground, and at a right-angle to the centerline of the car, and anchored on the outboard end so that it cannot travel transversely. The downrod should be more or less centered in the oval hole. The Clutch pushrod should be pushing more or less straight back and close to parallel to the ground. The TO fork should be centered vertically in the window, and close to the front edge of it with the pedal up.

Tips;
TO forks are BH and clutch-specific; you cannot just throw any fork into any BH.
BHs are somewhat body specific, in that the Z-bar mount is not always in the right spot.
The retainer-hole n the BH is somewhat transmission-specific.
The outboard Z-bar anchor, after the angles have been set, should be welded in place.
There is provision for an anti-rattle spring, down at the TO fork, which serves double-duty to pull the TO bearing off the clutch fingers. I highly recommend that you install one.
As for oiling, I have had very good success with a 50/50 mix of Dextron II orIII, and 80/90 EP gear-oil.

Happy Hot-Rodding