One seat done already finished up today. Ended up not to hard in design, just a lot of drilling and cutting brackets with my angle grinder. Still uses the original rail and as I said before mounts to two original pintara seat mounting threads. Also got the seat to be perfectly straight which is harder than you probably think!
Will do the other one tomorrow and take some photo's and put it in the thread. For you guys who have a bit of time and U12's, its a great upgrade considering the price of 2nd hand seats. The U13 SSS seats are the best bucket sports seat I've sat in (without being a racing harness altogether).