so wat do i do??
Just do as per http://www.miniriders.com.au/forum/tech-talk/19938-fastace-rear-shock.html#post194064 and see if a 550 can fit his crap shock. It'll still be HEAPS better, and the cost is SFA.
Later on he might want a better shock, and good chance the 550 spring will fit on a newer shock when that time comes.
550 or 800 springs: Just work out the spring length and internal ID is a match for the shock you will use.