I have stock seats, with a roll cage. Are there any harness solutions that would hook up to the horizontal bar behind the seats, then to the factory mounting spots? Thanks.

 

Lots do - in fact any harness should have the shoulder straps attach on a roll bar or a harness bar and the stock lap belt locations.
www.motorsportseats.com has a great selection and Jim is a good guy. I buy all my seats and harnesses from him.

 

http://www.motorsportseats.com/harnesses/3pt.html

I wonder how comfortable those will be with the top section going through the headrest bars

 

I ran Corbeau 2" four points with stock 03 Cobra seats for awhile (mounted to a harness bar). I loved that set up... the seats just weighed too much.

 

Schroth Racing makes DOT approved 4 points, you can even get them with an inertia reel. DOT approved harnesses are NOT SFI approved though, and in some places if you have a bar/cage they make you run SFI harnesses as well.

 

Would using 4 points with a stock seat be a safety issue since nothing is holding the harness from slipping past my shoulder? Or are these harnesses pretty fit

 

You have to have the right type of seat with the head rest to secure the shoulder straps. Schroth has it listed in their instructions.

 

Anyone try universal replacements, such as

http://www.seatbeltsplus.com/product/WSCH201P.html

 

You can use stock seats with some types of cross bars and harness bars.