Had the same problem 2 months ago, everyone was just saying "use steel strips and bolt them to the original mounting points" but I had no idea how. Eventually I fitted mine using 2 1000x30x5mm strips I bought at a DIY-store.
1. Remove stock seat. You will find that the stock mounting points are actually flat and low enough, but too far apart for most universal seat frames to bolt on to.
2. Cut one of the steel strips in half, measure and drill holes and bolt them onto the stock mounting holes longitudinally.
3. Cut the other strip so that it's wide enough to bolt transversally onto the other strips.
4. Bolt your universal side mounts on to your seat with the left hand side flipped to allow you to get it as close to the transmission tunnel as possible and mock it up on the strips.
5. Mark it up, drill holes and bolt the strips and your universal side mounts together.
If you have a non-adjustable steering column you will probably struggle to look over the steering wheel as your seat will be very low. I'm 6'4" and I had to actually lower the steering column to be able to drive comfortably. I also fitted an adjustable rail later, spacing the seat up 25mm and It's now very close to perfect.
These are the only pics I have, sorry.
