1998 trailer hitch

I have a 1998 villager with 150K miles on it, still runs great, I want to install a trailer hitch that I took off another villager, my problem is the mounting bolt holes have nuts tacked on the back side within the frame. The threads are really rusted and the original bolts are trashed.

My question is does anyone know the correct bolt size to fit this? There are 4 bolts altogther, also any suggestions on how to "clean up" the threads? I sprayed with master blaster but they are in really bad shape, other wise I was thinking of welding the hitch on?

any help is really appreciated

thanks

i just looked it up from curtis hitches website:

M12-1.25 x 35mm easily found at any home warehouse store

antiseize and lock washers along with regular washers would be a good recommendation

maybe a tool called a thread chaser will help clean up the thread holes; use grease or antiseize and hopefully that tool will clean out the debris