Frank,
As you have little or no preload on the fork spring, I would think that either the spring has collapsed or broken, or has at some time been replaced with a nonstandard spring. There were 2 options with the original springs - both were wound from 5/16" square wire, were 10½" long and 1¾" OD. with 25 turns. The 2nd option had the OD taper ground which resulted in a multi-rate spring. Now, Mr Douglas fitted these with the smaller diameter lowermost (which I think is wrong - multi-rate springs are normally fitted with the stronger end taking the shock load - to prevent the weaker end becoming coil bound - the usual cause of spring failure - which is not uncommon in the Mark series!).
Getting back to your forks, I would suggest further dismantling to find the cause of this lack of preload. Having removed the end-cap from the pivot, and the leading link, you should be able to tap out the pivot pin - this will then allow the piston (and linkage) to drop out of the fork leg followed by the spring and possibly a seating ring/spacer (they usually stay lodged in the fork leg). If your springs do not match up with the dimensions above, you will need to find a replacement. Unfortunately, there doesn't seem to be any new springs available at the moment, so you will need to enquire within the 'Douglas Community' for a secondhand replacement. Reassembly of the forks is simply the reverse of the dismantling (without any need to make adjustments).
Hope this is of some help,
Regards,
Eddie.