I suspect all Morgans will vary in respect of static rebound play Perry. Although rebound play is not desirable, worse is having static rebound spring pre-load. In this case the two springs are working against each other initially until suspension compression parts them. This situation causes the spring rates to be initially added as suspension compresses giving a very high spring rate dropping suddenly to a lower one. Exactly the opposite from ideal. See
here.
When measuring the static spring situation its difficult to achieve a consistent position even with dampers removed. Simon's mention of lowering each tyre onto two sliding sheets of ally (maybe greased) sounds good though.
I suspect your spring setup was no different before kingpins were replaced and it's only the recent work which has caused you awareness. FWIW I recently checked and found a consistent 10mm of play on drivers side rebound spring. Having SSL kit I was able to adjust main springs to zero this. This gave a noticeable improvement of ride over bumpy roads and less rattles.
