Wally Rust made some very nice harness bars for the firewall. They were under the GT 40 name, the same as the engine caps someone was looking for a while back. Wally is an executive with AutoZone. He was in California for a long time and moved, I think, to Tennessee. He has not participated here for Many years and j don't know if he still has his GT. Many of us got them. Presuming you want removable lap/crotch belts, many of us bought Brey-Krause mounting brackets used for Porsches. The seats need to come out and a slightly longer bolt sourced. The crotch strap goes from the brackets on the side to under your rump and then. Under your legs to in between your legs and into the harness clip. Nothing has to come from under your seat. Numerous companies make belts of various configurations. Mine are Safecraft (the same guys that make the fire suppression system for the GT). I don't think they make belts anymore. If you will be running sanctioned events, the belts will only be good for three years whether you use them or not. The 2 inch belts are better for using a HANS device.