'Standard' seatbelts

On my car I have one welded nut at the bottom of the pillar and one at the top.

So how are standard inertia seatbelts usually fitted on MK2s?
From looking at photos of other cars, it seems as though the inertia reel bolts at the bottom, the webbing then loops at the top and the end of the belt then travels back to the bottom (like any car), but it looks like it uses the same bolt as the reel?
I'm struggling to understand how that would fit properly. Am I just being an idiot?

How you describe, is how mine are fitted (although I have Pug 205 belts).

If your belts are old it might be good to fit some of these. http://www.paddockspares.com/sec50030-intertia-lap-and-diagonal-belt-for-outer-front-seats-of-series-hardtop-vehicles.html

I've already bought some second hand Securon belts, they're pretty good, they hardly look as though they've been used.

The only way I can see it fitting is if I use a massively long bolt with a huge spacer to bring the belt out from the fixing.
Otherwise it'll never fit up against the reel.





I could attach it behind the reel but then the belt will be all twisted further up?

If you want to use those belts you really need some sort of extension to either lift the reel up from the floor a bit or one that allows you to fix the lap belt away from the reel. It obviously needs to be pretty heavy duty though.
What you need is the sort of belts fitted to older cars that had static belts fitted originally. Not sure if Securon still list anything but something out of a 70's Leyland car might be suitable.

My Land Rover has the same belts,  they are fitted with a L shaped bracket and the belt end is bolted to the reel mount.
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Have a look round on Securons website. There are various fitting instructions on there this is one with a few ways to fix the belts.
http://www.securon.co.uk/fitting/extras/500fitting.htm

If you fit the lap strap behind the reel you need suitable spacers etc to allow the belt to swivel on the fixing bolt. 
Hope this helps a bit, sometimes a nose round a breakers can give you a few ideas.