John's 66 Dart GT covertible restoration

Hey guys. I got around to pulling the motor out of the Dart. I found these cast numbers.

Block - 2808030-273-7 What does the -7 mean? Also I couldn't find that casting number in any of the books I have.
Heads - 2843675-6
I found the heads to be 318 heads just wondering what the -6 means?
Head Gasket - 61018 and 2843680 They have the Chrysler symbol stamped in them. I couldn't cross reference any number back to anything.

I'm changing the intake so I wasn't worried about that.
Since this is a 273 block and it's not notched I'm thinking it has been bored to 318 spec's. Anyone have anything matching these numbers?