Thanks all for the input. I will clean the threads and measure the length but not run a tap.

I did run a tap on the rocker arm bolts from suggestions 10 years ago but was not happy with the looseness of the fit, although they have held. I believe the head bolt threads are a much tighter tolerance fit than over-the-counter taps (75%). I am afraid of loosing too much thread surface with a tap.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles