Rett, remember that Larry and Mike are the true experts, but I can give my experience and opinion.
First, the clear lip. Yes, you can pour it first with a clear and then pour the rest, but I do not advise it. In a pinch, like repairing a lure that breaks lips easy, you can make a mold that fits the lure and pour a little clear and push the lure into the mold to make a new lip. It is NOT as strong as a Lexan or circuit board lip, and it is tough to get the bubbles out of it unless you put it under pressure or vacuum the material first (strong commercial vacuum container). A less strong alternate that I use is Alumilite Amazing Clear Cast. It cures slow and the bubbles get out, but it takes several days to achieve full strength and, again, it is not as strong as lexan or circuit board.
Next, have I poured a bait with the lip in place before, and that is my preferred method. You not only get the lip deeper into the bait, giving it more strength against break off, as well as a stronger lip in general, but it is more consistent then placing the lip after the bait it poured.
I look at the bait and it does not seem to have a lot of detail, not any serious undercuts, generally a simple bait, in principle. I know a two part mold would work well, but I like your suggestion that a one part mold would work. Mike shows a video on Make Lure that he did where he molded it all at one time and then used a fillet knife to open the mold to remove the blank. If I recall correctly, Larry did a couple like that as well.
It looks like it was made of wood, so my question is how much, if any, weight was added to the original. If the bait sets low in the water, it might be a great bait to pour using straight Alumilite White in the bottom, then Alumilite White with an equal amount of Microballons for the top. This would right the lure easily, especially with the hook on the bottom. With what looks like a wake bait type lip, it could be a perfect option. Alternately, one could add weight to the bottom and use Alumilite Foam for the top.
Because it is hard to explain how I would test the lure for center of balance and calculate the amount of weight and buoyancy needed, it may require a little trial and error. With that in mind, I would use HS2 with thicker walls. Alumilite Foam tends to compress and push HS3 a little too much for me and I would want to keep that option open, so HS2 is my suggestion. If I wanted to use a two part mold, I would actually use Quick Set for this one.
I know that I am getting into too much detail, but ....... this is kind of a fun project to look at. Pour from tail, vent at nose???????
Hmmm, how can I get a couple when you are done?