Your right, the Gaz shocks are the one's to go for but I was after a spring to run with a standard Triumph shock.
The shock just do the damping it's the spring with do the work
There must be a suitable spring out there some where.
You have pointed out the standard springs on a 4 pot is 150lb so there a start.
I'll try getting some shorter springs rated at 150lb and see what happens.