I don't have my SVA manual yet.

Can anyone tell me how height the belt mountings need to be and where this is measured form?

I think this is it.
Rescued attachment seatbelt.JPG

how high can the recoil be mounted, the bit that holds the wound up belt (sure thats not the name for it but on the 3rd can of lager) Just that i need to move my seat back & seat belt it mounted in the way. ummm lager !!!!

i'd not bother with standard belts.

i can manage to nearly drag myself out of my mk bucket seats, with lateral g, with 4 point harnesses. a standard lap and diagonal won't give you the required support imo. i'd look at fitting harnesses really.

i'm not saying it's the definitive answer, but it's better to find out now, than when it's finished
tom

point taken
cheers