The clutch noise could - as well as being the spigot-bush, or something more serious - indeed be the new release bearing fitted being dry. If so it needn't be a gearbox out job, it's quite possible to sparingly and accurately direct spray-grease in through the clutch fork opening (and the identical opening on the n/s of the box, if present) onto the bearing without in any way contaminating the driven plate or flywheel.
It's worth trying before heaving the box out again. It worked for me in early 2013 with an excruciating squealing when the clutch was depressed from the day the car arrived, and didn't go away with regular use, and since, well up to 2018, when the car was taken off the road to tackle the corroded inner-wing, I'd never heard so much as a peep (squeal) from the release bearing again.