The problem with baby stays for lateral stabilization, is that the attachment point of the stay to the boat must be precisely in line with the pivot point of the mast. Otherwise, they will prematurely tighten or loosen. There are many systems that folks have rigged to accomplish this. The Precision 18 is reasonably close in design to a 19, and I know there are some discussions of this for the P18 if you google around.
One thing you could do is to get a sliding gooseneck fitting from Dwyer, and rig some rigid supports. Some have used pipe with the ends smashed down into flanges. They could potentially be rigged to attach to the chainplates, but even though the chainplates are abaft the pivot of the mast, because the rigid pipe attaches to a sliding gooseneck fitting, it is allowed to slide up and down the mast track as you are raising the mast.
What I did with mine, was to take an 8' 2x4, and a 1/2" square U-bolt (trailer mount bolt.) I cut this in half to make 2 L shaped pintles in the 2x4. The top I used plywood to make supports for a bow roller. Now, I put the 2x4 into the rudder gudgeons, and lift the mast onto the roller. I can then easily roll the mast aft, to get the pivot bolt into the mast step. Then, the mast is already hosted roughly 1/4 to 1/3 of the way up by the tall support. Provided the stays don't get hooked on hardware on the cabin top, the lift isn't all that bad. However, rigging a gin pole and using the main sheet tackle or vang tackle could make the lift even easier. Not tried that yet, I'm still muscling it up.
The mast drop onto that support was easier than expected, because I stood in front of the mast facing aft, and straddled the mast as I lowered. It went down really much easier than I planned, and it wasn't that hard to guide it onto my V profile bow roller. You could make such a support using a keel roller that is significantly wider than my 4" bow roller, actually…
As far a gin poles go, I've seen them with winches on the pole that winch the mast from the gin pole, and I've seen them where a halyard attaches to the gin pole, and stays only one length. Then the tackle attaches to the gin pole and pulls down to the stem head fitting. The gin pole can remain 90º to the mast, and still have room for the tackle, because the mast step is up on the cabin, and at fully up, the gin pole would have a gap between tip of the pole and the deck level.
Brian