RE: Bubbles in the over flow tank
You're jumping the gun again, Matt.
Some bubbling in the coolant is normal.
When are you seeing this? When the engine's at full operating temperature or when it's cold? What aspect of the bubbling has you worried?
-Are you losing coolant?
-Is the engine overheating?
-Now that the ignition problem is fixed, how does it run?
-Have you pressure tested the cooling system? (A pressure tester is ~ $50 at any auto supplier, and it's commonly used tool everyone should have anyway).
-If it's head gaskets, the exhaust will smell like burnt sugar, and if they're very bad, it'll be thick and white.
So... how's the exhaust?
Dave's right: head gasket problems in Mark VIII's are really, really rare.
Still, cooling systems with screws blocking off important tubes should get fixed!
Coolant MUST be able to circulate in and out of the reservoir. It's not just an old style "puke tank". It's an integral, sealed part of the system.