I thought you were asleep and was re writing my post when you posted, that's why it's gone. But you have it quoted. I see it's 5:30PM there, sorry.
It is possible that you have a tapered head with non tapered plugs that "seems" to fit. That is what we are both thinking. That's what Turbobill said way back. If that is possible, you don't want that. Others will chime in tomorrow. BigBlockV6 has a post talking about tapered for larger motors. D10 plug.
ALSO: Your spark plug hole picture does not look right at all for 305. Is that a weld fillet holding in an insert or greasy spot painted orange? What the **** is that? It's either what Big V6's look like or it's a
fix. That's what FMAP said way back. Show a hole in the other head.
Thanks to K
for asking for a picture.