Since the 1985 DS II has a hinged maststep, it should not be hard to step/unstep the mast while the boat is in the water. I made my own mast crutch to use while trailering my DS II, I can look up the measurements and post them. It ain't fancy, but it works!
My 1979 DS II still has the original "keel-stepped" mast (actually, cuddy floor stepped) and I have always (well, 95% of the times) stepped/unstepped the mast with the boat in the water, it is easier for me to do it that way. One tip, if possible, can you leave the mast attached to the boat while under the deck? In other words, most people who trailer their boats often just unhook the forestay and lower the mast, leaving everything else rigged (just the 2 shrouds on a DS II). The mast could be unpinned from the hinge and slip forward if needed as long as it is secured. This would also allow the mast to be layed lower than if kept pinned to the hinge. That way you just slide the boat into the water, raise the mast, attach forestay and hoist sails (well, you will have to bend on hte jib if you are using that day.) the mainsail could be kept on the boom if you have a cover for the sail. Then just slide the gooseneck into the mast slot and you're set. If I remove my boom during the season (boat is on a mooring) I'll just unshackle the downhaul (I added that shackle for that purpose) from the boom and remove the upper mainsheet block from the boom, saves time when I re-rig the boom.
I've attached several pics, the drawing is my crutch as is the one inside our garage. The red boat with the grey crutch is someone elses home-made setup. The red boat with the low crutch shows what I believe to be an O'DAY original optional part, this was part of the "trailing Package" and was made from 2 pieces of wood using a set of standard rudder pintles to attach to the rudder gudgeons on the transom. It appears that the other owner also used standard pintles, I used bend lag screws (heads cut off) to save $$. Finally, the pic of a yellow boat on the trailer shows SUNBIRD ready to head for the ramp, as you can see, my crutch does hold the mast up a bit high, this wil lbe fine for supporting the mast as you step/unstep, but might be a bit high to fit under the house deck? My mast lays paralell to the top of the cuddy and my crutch could easily be used if I had a hinged mast.
