Yes, it is involute, I took the original gear and replicated it using a number of measurements and a fair amount of math. Then I drew it in CAD. I milled this top down, not a traditional hob style machining, so you'll notice the root of the teeth is circular rather than "flat" bottom. It's not perfect, but it should work. I used a .0625" end mill for the teeth, machine time for the teeth alone ended up being over 4 hours as the tool is so small that it moved like 1.5" per minute, and had very small step overs and depth of cut. I just let the machine run and went to bed. The rest of the machining was like minutes. So maybe 5 hours to make this, but I was asleep for the majority of it. Hopefully it works. If it does, I will make another one, and it will be better yet.
The cylinder head is next to hit the mill. My father almost has one of our two spares totally welded up. He's going to drop it off Saturday.
There is a press fit TDR/GT water pump (steel) gear from BDK that looks nice, but we didn't want to have to deal with the press fit because by the time we sent our water pump shaft to the UK, buy the gear, pay for return shipping, etc., it just didn't make sense to do it. I saw posts from the aluminum gear but it doesn't seem available anymore. We also wanted a gear that could be inspected, removed, replaced, like a stock gear. So here we are. Of course we did buy the high flow impeller and cover from BDK, they sent use the wrong stuff...