all i did with mine, (mr2 seats) run angle-iron across front and back on original floor mounts, removed brackets from seats, sat seats on angle-iron and then welded rails to the angle-iron

Be really careful when fitting different rails to different seats, like datsun rails to Toyota seats, my engineer mate said that it is very difficult to get them mod plated, which all aftermarket seats have to be.
ty

I must agree with Ty. You really need to spend some extra coin and at least get an engineer to design your fabrication. Then maybe you do the work and get the engineer to mod plate it for you.
Seats must be mod plated