Why not just take some carb studs that are slightly long and grind them down a bit on a bench grinder (don't forget to re-chamfer the end)??? Grind the studs down enough so they won't interfere with the carb...
I agree. If you don't have threading dies, what I do is thread one or two nuts onto a bolt I'm cutting. Then after grinding / sanding the end "clean" you can unscrew the nuts "a few times" past the end and smooth the threads.
Also put the cut end into the manifold, so you don't fight it every time with the nut.