Thanks swooshdave, that chart is exactly what's required! I'll measure the pistons and work out what's needed.
My V50 with it's original linked brakes has a copper brake pipe for most of the run to the front (as suggested by 68c)
I know from previous experience of owning my Magni, that if the linked brakes can be well ballanced, the set up makes for very controlled braking. Like the V50, the front lever is redundant in most braking situations.