Rear Tub floor an Gearbox.

1 What do I use to fasten down a new floor on the rear tub of my Series 3 land rover 88 inch
2 Who can I get in contact with to have my gearbox repaired. I live in Cornwall but happy to send it anywhere.

Mushroom head bolts or blind rivits.
@jamesmartin is the gearbox guy on here.

Do the gearbox yourself sounds scary but have a look inside its actually pretty basic.
Theres a good vid on youtube of a Kiwi guy (I think) putting one together.

Thes have a good reputation
David Beaumont 4x4 Gearbox Specialists
R Whitehouse & Son Reconditioned Gearboxes
Simmonites do exchange
landrover specialists simmonites gearboxes
these also Land Rover Transmissions Specialists

Is it possible to use sealed blind rivets or won't they be strong enough.

Rivets are what Landrover used.
They go into the tub crossmembers underneath.

Thanks for that, I will look up David Beaumont 4x4 about my gear box. Hope u all keep safe.

Sealed blind rivets are fine. Get some Cleco clips, get a set off e-bay - under £30 for a set of clips plus the tool. You need 4.8mm rivets and the matching clips. Get and air-riveter if you have a compressor or lazy tongs. The 4.8s take a bit of force. M5 button head cap screws look very much like a rivet if you ever want to take it apart again.

I use the all the time.