How did you attach your 3 point retractable seatbelts?

I did not. I ended up returning them. The seatbelts required a hardware kit that does not come with the seatbelts. The expectation is for you to drill and install the hardware behind the drivers seat. I have the Wesco lap/shoulder belt setup in there. It's not retractable, but it does work. It's just more cumbersome to work with.