David,
As an update, I noticed a number of different seats used when I was at the National Rally - Metro, Marina, XR3i, (Saab - mine), I'm sure there were some Newton (they don't look too obvious!) etc. Basically it's the seat mounting that needs the ingenuity. Find some that you like and see if they fit (width and height).
Dunketh, as I wrote, my seats were fitted at JLH - I didn't get a kit, so we may be talking of different things - the seatsrails were fitted onto a "top hat" section of steel sheet which was then adjusted to the correct height off the floor (angle grinder & welder), then bolted to the original bolt holes at the front and the floor at the back. Not exactly
just some metal bars bolted together then bolted to the seat!
things may have changed....
However, I'm really happy with the mounting - It's much stronger thtn the original... plus I have seats with head-supports. One of my work colleagues has just had her car written off by a rear end shunt, so I feel much happier with them in.
Colin