Since you cannot get Barlow winches anymore, you are best off with something like a Lewmar #6 or #7. They essentially are the same winch, but the #6 has a lower profile. The O'Boy 192 is not a very big boat, so someone maybe thought they didn't even need a winch for the halyard, which probably is true. But, if you want a winch, then I suggest the ones above.
The great thing about a mast winch on a small boat is that you only need use it like a capstan without the handle. The handle isn't needed.
On my boat, I merely run my mainsail up, take three wraps around the drum and while standing in front of my mast, I just pull the snort out of the halyard and get it tight. This action is enough to get my sail up as tight as I need to get it. Then I push the halyard into the open clam cleat above the winch with my left hand and pull the wraps straight off the drum with my right hand and cleat it off.
A small boat sailor can't imagine how fast and simple this can be done until he has had a sailboat with the mast set up this way.
Doing this without a winch, you would need to run the Mainsail up, take a turn on the cleat, pull the halyard out and try to hold what you've got while you re-cleat the halyard and you may need to repeat this two or three times until you get the wrinkles out of the luff. I think that this task can be simple without the winch if you can mount an open clam cleat somewhere above the winch plate and your existing Main Halyard cleat. You'll need to mount the open clam cleat so that it is not in line with the halyard, but about 1" to one side of it. Although, the placement of the clam cleat will be uncertain until you've mounted your winch to the mast so you're better off holding off on it until you get your winch mounted. Later on if you're able to find a winch for your mast and get it set up with the clam cleat, I think you're really going to like it as much as I do. You'll need to get a winch with a drum that has enough area for three wraps of the halyard to avoid any "riding turns."
Joe