Series 3 Transmission Noise,diff,prop,box or ??

Hi, new to here and hoping someone can help diagnose my transmission issue.
Series 3, 88" 1982
Problem is in 2WD the landy feels rough and there is a vibration in all gears, gets worse with speed and load
If I put in gear and roll downhill, forward or backwards, with the clutch depressed there is a clunk, clunk, clunk in all gears, high or low range, but not in neutral, sounds to come from the gearbox area but difficult to tell.
The landy has recently been put back together, all mountings tight, all oil fresh, new u/Js
If I jack up the rear wheels and run in gear can hear more of a graunching sound than a clunk which sounds to come from the handbrake area but with a screwdriver sound more like the rear diff bearings.
Wheel brakes are free
Handbrake is free
Rear Wheel bearings are fine
Taken inspection plate of back of gearbox, tiny amount of play between shaft and gear but very little.
If I remove the rear propshaft noise goes away
If I drive in front wheel drive, with rwer prop removed she is fine
Taken out rear diff, looks and feels fine, no play smooth to turn
No significant wear in half shafts / flanges
Rear propshaft looks and feels fine
Gearbox rotated by hand in and out of gear is smooth but there is some backlash and if I rock the rear output shaft backwards and forwards I can simulate the clunking when rolling
Was planning to swap front and rear diffs, but having removed the rear and not finding anything thought I would check for other ideas here before going further.

Any ideas, I'm stumped!
Thanks
Dave

hi have you got prop shaft uj in phase there should be 2 arrows on each half that should be in line it to me trubel could be in rear diff have you undone dif crown wheel bearing caps and inspected cones and cups for pitting etc if you pull crown wheel right out take off prop you could find suatabel socket and spin it up with electric drill some years I had quite a loud noise in my lt85 gear box on close inspection the in put shaft had small pit torning it by hand it took me some time to find problem if you grab transmission brake drum is there any play between it and out put shaft isnut on out put shaft tight to rule out diff you could as you stated change it with front one

Hi, yep the u/js are in phase, haven't checked the cups / cones will add that to the list
No play between transmission brake and output shaft
Just come in from swapping the diffs over, will tighten everything up and give it a whirl tomorrow
Thanks

is there any play in rear out put shaft

hi hope info might help let us know what you found just a thought have uoy wa tched rear prop shaft shaft spinning while you drive wheels off ground it is best to take off wheels when spinning up prop but make shore you have your drums fixed tightly to hubs when you rebult uj is it possible that one off needle rollers fell out with you noticing it? if you strip diff as well as checking all bearing surfaces with magnifying glassalso check crown wheel and pinion for damage etc. could rear prop be slightly bent 40 years alalhad a themes trader truck mixer it was a 6 wheeler with awd conversion this ment both rear props were locked together over back axel there was a bearing box to take drive to back axel the oil seal went filled with water going down roadbearing box seazed up stoped truck mixer dead on fitting new box there was terrible viberation took off rear prop perfict now inspected rear prop could not see any thing fitted new prop now perfect old prop shaft must have been twisted out of line mounted prop in lathe still could not see any thing rong moral of story is some times you just cant see fault but subustion with other part will prove it please excuse spelling left school 61 year ago