Mite try 12-24 ordered some screws, tap. Will practice on a some scrap steel first. Wanted to use 12-28 but cant seem to get that size of screw ??
My thoughts on that are that it's going to be a bigger, uglier hole.
By changing the pitch, you are risking chewing out the hole worse than it already is. Unless you re going larger enough to get past the remnants of the threads that are there already, which I don't think you will with a #12.
It's looking like a pretty good case study for the theory behind "don't f**k with it in the first place" Just sayin. And yeah, I know it's too late for that.
Think lots, move slowly, and plan it all out carefully, or you'll be looking for a welder to fill the holes in next. Aside from that, I think you are better off with a fine thread rather than the coarse series.
Oversize, at least, up to a point, screws, are not tough to make if you have the correct tools. Dead easy to adjust a die head to make an oversize 10-32 screw with the standard size chasers. Single point cutting oversize screws is not tough either, but if you have to pay someone it can rack up some hours of careful work. It's a better job for a guy that can do the work himself, or in conjunction with a friend that has the tools and skills.
At this point, I suspect that your best option is to install the 10-32 screws and torque them up, use some thread locker. Deal with the resultant hole if it strips, but not before. Refer back to the basic rule of "don't...."
Cheers
Trev