Bolt Size for Water Neck and Ignition Coil

Doubt they are metric. Probably just corroded threads in the manifold. All you need to cleanup threads is a cheap tap set, especially in aluminum. Get the cheapest one at Harbor Freight. The bolt is probably 5/16 coarse thread. Try the tap, but don't force it too hard or bend it sideways because a broken off tap is not fun. Keep going back and forth with it. I use WD-40 for lube on aluminum. Aluma-tap fluid is better. If the tap goes in fairly easy, that tells you the bolt size. Blow out the holes with air. You are lucky the auto parts guys didn't laugh, since Ace Hardware is a better place for nut & bolt questions. In fact, I would buy stainless bolts there to look purty (I did).