I used Sabelt 500/30 (as recommended by others on here). I got them from Paddock Spares - they are intended for Series Land Rovers and include various brackets etc. which enable them to be fitted satisfactorily for a 500, though I did have to reverse the orientation of the tongue by folding over the belt and feeding it through (does that make sense?). All existing mounting points used on my 1971 500L