Which seats? Are you using Hans?
The big advantage of the McLaren harness is that the inboard lap belt goes into the seatbelt point, and the outboard has a quick link that attaches to the seat rail. Other than that, any 5 or 6 point will work.

 

If you have the Senna seats, the sub belt bolts to the seat frame near the back on both sides. Not sure if you have the harness bars. If you do, there should be two sets of clamps that bolt on to keep your belts in the correct positions. If those aren't present, I'm not sure where you'd tie up at the top. As Invisible mentioned, the lap belts are very easy to attach. McLaren supplies Sabelts, which worked perfectly for me. I don't know if you can order the Mac compatible set elsewhere or only from a dealer.

 

You can buy the OEM version in the UK, without the McLaren branding. I think it's Apex that sells them, they're a lot cheaper than the McLaren branded version. The original harnesses are much nicer than the aftermarket versions, the set I have is from a Senna with carbon trim on the camlock. The webbing is also better, it's flexible like seatbelt material, the aftermarket ones are thicker, and the buckles are some sort of lightweight alloy. The webbing is 3 inch though, so doesn't work well with HANS.

 

I have the Senna seat with the harness bar, just missing the entire set of harness that the car should came with...

Thanks for the information, just have to figure out whether its worth it or not😇

 

It may be worth it, proper fit, should include all related hardware like bolts and bushings so the belts can rotate freely on the mounts. Also will last you for years.

 

It's pretty easy to replicate the fit. You can buy the bolts on Amazon that allow rotation, and you can get 3500lb quick links from Tractor Supply