How did you make the seat brackets?

 

I'm also looking to replace the original seats in my '02 R53. Way too much sliding around (in the seat) at track days. Has anyone tried the Sparco R505s?

http://www.sparcousa.com/pseats_street.asp?id=714

 

WOW those came out nice!

 

after taking the mounting supports off from the seats one side of the rails all i did was drill the exact size holes and welded in the holes where rivets were holding the old brackets. so no brackets were needed for one side of the rails. on the outer side of the rails i added a 2x2-3/4 by 3/16 or 1/4 thick of flat piece of steel and it was welded on all four sides of the bracket for good bonding. my friend who helped me do the swap is a certified welder so his put on some good welds on there and then drill the mounting holes.
i'll share pictures after i upload up them.