What size header bolts for a 72 340?

fire_medic said

Thank you, yes it is pretty tight on a couple of them. Had a hard time getting to the Allen heads. It was a real pain. Took me over two hours to get them off. : (
Any tips or special tools that make it easier?

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There are a couple where it helps to put a small dent next to them, it's easier to get a wrench on.

But, look at the ones I posted, I used those and it was pretty straight forward. Put a dab of neverseize on them when you put them in.

Non hardening sealant on the front and rear ones as they go into water.