I noticed that you have a system to raise and lower the mast crutch. Unfortunately, I don't have a lot of design time and will have to drop my mast this weekend.
I trailer 3 to 5 thousand miles a year and don't care for the mast to be resting on roller all of the time. The adjustable roller also comes into play when I drop the mast since a little wind or slope makes it impossible to hit a 3" roller because the mast, at that point, can move 6" side to side. I can step back to the stern hold the mast with one hand in position and raise the roller to accept the mast. If you have extra people and rope another method, we use around here, to keep the mast straight on the way down. Hoist 2 lines via the main halyard to the top of the mast that are long enough for people to hold and stand off to the side of the boat (out of the danger zone). Position a third person behind the boat, again out of the danger zone, to call instructions to the line handlers (Bob tighten, John loosen, etc) to keep the mast straight. We raised 2 over 30' mast Monday this way, using a gin pole, one with the mainsheet and the other with trailer mounted winch and turning block.