hi i have 2 y-blocks the 1 that came out of my 58 and the one i got for it the old motor has ecz g on it and the new one has cia e i would need to do a valve on either set of heads which is the better heads for a 292 60 over with a mild cam and a 600 cfm carb on a 57 intake?
As others have said the ECZ-G heads are the better ones and further the '58 heads are likely to be posted if they are original. If they are posted it means that you can safely mill them up to maybe .060". This would raise the compression of your engine considerably which is all to the good. The stock CR listing for 58 292's is something like 9:1 but is is actually considerably less. With about .060" off the heads you would be near 9.1:1 or so depending on the deck height and head gaskets you use. This will run fine with unleaded premium. If you decide to do this you need to have about .040" taken of the intake manifold surfaces of the heads.
What ever you do you need to be working with a pair of heads not one ECZ-G and one C1AE.