Brent. Unless you are seeking to make your car as original as possible, I'd recommend using a set of ECZ-G or 5752-113 cylinder heads. That said, the ECZ-C heads you have are decent in terms of combustion chamber size (compression ratio) and street performance (drive-ability). Just sayin' . . .
This stuff is getting sooo old, that most people looking at your engine won't even know what it is, let alone whether the heads are the 'correct year' or 'original application'. The fact that you've got the correct species of engine makes the car noteworthy. Unless you go to a C.T.C.I. meet, so many 'Birds have had other engines stuffed in them whether they be Ford small blocks, FEs, or other makes.
Compression ratio makes a lot of difference in stop-and-go driving and engine torque in accelerating to pass or speed-up on a highway entrance ramp. In rebuilding these engines, most of us are using the newer composite gaskets which seal better and stay sealed, but their thickness reduces compression ratio by increasing the effective combustion chamber volume. Remember, too, that the manufacturers' ADVERTISED compression ratios AND horsepower figures from back-in the-day were theoretical calculations not measured or verified by anyone.
IF you haven't seen it, click the link below to view John Mummert's info on y-block head specs.
http://www.ford-y-block.com/cylinderheadchart.htmFood for thought . . .
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York