My engine showed up from the machine shop with a missing main cap bolt. Went down to fastenal and got a grade 8 bolt. No problems. I wouldn't hesitate to do the same for the head.
On a 216,235 0r 261? Other than the rear main, the main caps are only located by the shoulder near the top of the bolt.Without the proper bolt the main cap can fret around and might cause a bearing failure.
