Are these the bolts with a short shoulder the hood linkage pivots on? I seem to remember the diameter of the thread being 5/16", don't remember if the thread is coarse (18) or fine (24) threads per inch. Try one of those two taps, and if it gets tight after a turn or two, try the other one. Chasing the thread shouldn't require much more effort than a firm twist with your fingers unless they're badly rusted.
Jerry
