The noise you hear after you put it in gear that quiets down after you get going.
Do you hear that same noise, or one very similar, when you step on the clutch pedal before you put it in gear? Then you have the grind/crunch as you put it into gear. And does the noise continue until you let off the clutch pedal?
If so to either, but especially if the latter or both, your throwout/clutch release bearing is going or gone.
Could be critical or not, depending which type of bearing you have.
The bearing usually sits there not doing anything while the clutch pedal is up. Its function is to move forward when you step on the pedal, and it then engages the levers ("fingers") on the back of the clutch cover and pushes them forward to pull the pressure plate away from the clutch disc allowing it to float between the flywheel and the pressure plate (which is when the shaft can then slow down to a stop so you can shift silently!).
There were two types of bearings used on the SuperC. One was a simple block of graphite (think VERY HARD pencil lead) mounted in a cast shell (the carrier) at the rear. The graphite face engaged the fingers. Graphite having its own lubricative properties, the fingers, driven by the motor, would spin around on the face of the bearing while the pedal was held in, making their own sort of seat or groove in which they could "nest" and spin.
The other bearing, which is more typical, especially in automotive applications, was a roller bearing. The outside was held by tension into the carrier, and the clutch fingers met the center section which was free to spin up to speed when it met the fingers.
Either type making a fairly steady FINE grinding sound is not an immediate problem but will need fixing. In the case of the graphite bearing, the fine grinding sound is likely from rust (how long did this tractor sit?) on the face of the fingers grinding away at the graphite. In the case of the roller bearing, those fingers, whether clean or rusty, are grinding against the center of the bearing which is not turning, wearing away fingers and bearing face.
If the noise is more of a thumping or banging or harsh chattering that you can feel through the pedal, a good chance you've got the graphite bearing and it's missing a chunk or two out of its face. Not to be an alarmist, but that's a more urgent repair as the fingers will either tear the graphite block apart leaving you with nothing or the block may actually break a finger on the clutch cover should it break in such a way as to fetch up just right.
To figure out which kind of bearing you have (Sorry to be so long-winded, but this stuff isn't in the books). . . There's a round hole on the left side of the motor end of the torque tube, about two thirds of the way back the bell, that may or may not have a cover over it (simple spring clip holding it in, pops right off). Normally that's the hole you use to get in and grease the carrier for the release bearing. Put your unskilled helper up in the seat. While you shine a light in the hole (or maybe shine the light up through the oval hand-hole at the bottom of the bell, just under the flywheel), have your helper press and release the clutch pedal and adjust your light around so that you can see the carrier with the bearing move back and forth. It's mounted in a fork made of a flat strap of metal bent for the purpose (you'll only see the near, flat, side of it). If it's a roller bearing, you won't see much on the forward side of the carrier as it comes into the fingers. The graphite bearings had a slight conical shape to them and extended a little further forward out of the fork and carrier than the roller type. The cone may not be evident just because crud and gunk will have accumulated on the sides of it over the years. Looking through that hole, if the carrier appears to be pretty much up flush to the clutch fingers before engaging them, you have either a roller-type bearing or a badly worn graphite type that needs replacing anyway. If you see any significant amount of material (graphite caked in gunk) forward of the fork when the fingers are engaged, then it's likely a graphite bearing, and the type of noise (fine grind or chatter) should guide you in how urgent the repair should be.
If the throwout bearing does need changing out, that would also mean splitting the tractor just behind the motor and there'd be no time like the present (whether that comes sooner or later) to deal with the pilot bushing. That could be as simple as cleaning it and putting the slightest dab of Never-Seize into it or just replacing it. And you'd want to likely check out the clutch cover and pressure plate and replace the disc while you're in there.
