Hey Brandon,
When going with the helicoil option you are actually going to have to go with a bigger hole anyway to allow for the room for the thread insert itself. So if you have enough real estate to work with, a bigger bolt is a good option. Just make sure that you drill and tap the holes straight and you will be okay. On the ones that are thru bolted, is it possible that you could use longer bolts and put lock nuts on the back?
FWIW..........I have been around machine repairs most of my life and I do not like helicoils. There are other options out there that are somewhat stronger.
Here are the ones that I prefer:
EZ Lok
http://www.ezlok.com/InsertsMetal/carbonSteel.html