Not worth restoring.
By the time you find ALL the bits you are missing it will cost more than a tidy s1 and at the end you will have a patched up s1 that's not a matching numbers car.
I broke a s1 last year and bonus balled another,yes they are valuable but the folk looking for the valuable cars are wanting nice shells,matching numbers,tidy interiors.
A good dash is £450 up to £1000,a rough set of seats is £500 plus,factor in a kit,welding,respray,loom,gearbox,bronze glass,sunroof,wheels,arb etc and it will bankrupt you.
If you can find a worse s1 that's complete it's worth doing maybe but even a rough 1 is 5k upwards,going by eBay anyway.
If you have the v5,floor number and vin tag sell it on is my advice,prob worth £600 as it is plus your lhd shell.