Years ago, most likely.

What I'd do is figure out the correct size and then buy new Grade 8 bolts and screw them in. IIRC the head bolts on my 318 were nothing more than Grade 8. The only bolts on the engine that wouldn't be OK for using Grade 8 are the rod bolts.

Don't make this any harder than it is naturally.

R.

A Grade 8 bolt will have six lines or tick marks on the bolt head.