Our 1985 4/4 came from the factory with static belts, I recently fitted inertia reel belts.
All of the fixings were the standard 7/16 UNF seatbelt thread into captive nuts.
The original fixing through the top of the wooden wheel arch on our car is a 3/4" thread nut and bolt drilled & tapped 7/16 UNF for a standard seat belt bolt.
I found that the new seat belt buckles needed silicon spray ("Mr. Sheen" in the UK) to make them release easily.
