Not very good with these forums! I have posted problems on another thread, wrongly!
I'II start over.
TD5 Defender 2001, had a new chassis after purchase, anything worn was replaced, bushes,clutch,head gasket, injector loom, it has now been fitted with new BFGoodrich all terrains on boost alloys,all balanced and tracking set, new front prop.
Driving with front prop off still had vibration,driving with rear prop off no vibration, so replaced rear prop, vibration still there. changed oil in transfer box and rear diff, removed rear shafts checked for any wear, nothing found. Driving vehicle with diff lock in high,vibration seems less noticable.
My only thought now is transfer box.
I had the transfer box rebuilt on my other 90 but that was because I smashed it up on a hill climb, that one drives lovely!
Any thoughts or suggestions appreciated.

At a guess I'd say rear diff or transfer box as you've shown the problem is in that area

Can be very hard to diagnose faults like this

Thanks for your thoughts. I discounted the rear diff because with the rear prop disconected there was no vibration, and the gears are still moving being driven by the rear wheels rotating!

Diff will still be turning with the prop off

Very difficult one to diagnose sadly