Not sure I know what you mean by "do the bolt". It's the second of two carb mounting bolts and this was the whole point of drilling and tapping it out. So if so, yes, a bolt will be going back in. As for finding a junked case, I know of only one guy who keeps everything,but I doubt he would have a specific one. I'm frugal, but not that frugal to spend months looking for a used engine. I'll buy a horizontal and convert.
Now the high temp epoxy, JB Weld Extreme Heat, is rated for something like 1000 deg F.
What I mean is install the bolt that n the outside so there’s not perennial blow by going out of that hole. Sure there might be a little blow by around the threads but nothing like leaving it open.