If you aint got clips on the end mate just bolt them to the hole in the boot floor. i've got a 172cup and theres two holes under the carpet just behind the rear seat, I just used this with the same bolt that holds the seatbelt on the door pillar in the front of the car so should be strong enough (i've done 15+ trackdays like this). If you dont need your rear seatbelts just use another bolt to secure it in the seatbelt release clasp hole. I dont think its safe to put them in the same point but I may be wrong, and tbh if you are using harnesses a cage is advisable as you are fixed in position if you tip it over and can't lean forward like with seatbelts, but plenty of people do.