I just did this on my friends tricked out BMW 2002. He got Cerullo racing seats and whe had to make brackets for it and we attached the harness to the existing seatbelt hole. For the crotch strap we machined a bracket that went under the seat for it. About 2 weeks ago he had a cage installed and the harness is mounted to the cage now. He has Simpson 5 point harness with quick release they were like $180 and they are pretty bad ass.
Eric 97 Eclipse GS Red Mods: Hotshot intake and header Matrix Cat-Back 17 inch Konig Tuners 1.5 inch Progress Springs Tokico Illumina shocks And a bunch of interior crap