Still to hear what happens with clutch in, going straight from neutral to reverse with engine running at idle and perhaps say 1,200 rpm.

Additional test. Place in reverse clutch on floor, engine running, transmission.gears are all stopped. Move to neutral, wait a couple of seconds leaving clutch pedal on the floor, move back to reverse. Grind or no grind? If grind, either clutch drag or pilot bearing drag. 40 seconds for all of above.

The answers to these might/would eliminate much irrelevant speculation.