Yep, good advice from the guys, Rossco, I have sourced suitable shocks, off a twin shock roadie, from wreckers, the spring rate needed depends on a couple things so it's a bit suck it and see.
If ya get stuck , I have a couple of 350mm or 13 1/2 " you could try for size, just cover the postage.
You would have to sort the eye bush size out , oh yeah , another trick was to weld another eye on the top mount of the shock so you could alter head angle slightly if needed.
Oh yeah , bling, they are chromies with a short chrome top spring cap.
Let us know how ya go
How about a pic or three of it !!
Foss