I just bought a FE engine with casting C6ME-A and heads with casting C8AE-H. The heads are drilled for 390GT exhaust but the casting number cross reference to a standard 390. Could I be miss interpreting the casting numbers? The exhaust manifolds were hard to find since the bolt pattern is different. I though I was buying a standard 390 with CobraJet heads. Not sure what I have?

 

Well they are certainly not 428cj heads, i don't remember off hand but i thought the gt heads had both patterns allowing either manifold but don't hold me to that.

Well I just looked at some pics showing the inner 2 ports not having both vertical bolt holes.

 

Heads

They list two heads for that casting number here, 8 bolt or 14 bolt.

 

both having grandma performance qualities, i would drill and tap the gt heads to accept vertical pattern and gt. Then headers are a go.

 

The diagonal exhaust bolt pattern heads were used on mid size cars like the Torino /Fairlane and the Mustangs & Cougars that were equipped with FE's. They had skinnier engine bays compared to the full size cars and trucks. I've also seen them referred to as "390GT" heads. If I recall correctly the 68 heads were the first ones cast with the thermactor lump in the exhaust ports (Cali smog pump cars) but not all heads were drilled for the air injectors. They are typical FE heads, performance wise they are about the same as the later D2TE-AA heads.

Just as a thought before you have the extra holes drilled for the vertical pattern, if they are a matched set of heads in serviceable condition, you might be able to sell those 14 bolt heads to someone doing a 390GT car restoration for a good chunk of change to put towards a pair of Edelbrock aluminum heads or something else more in line with what you're wanting.