If you can get a GX head, use it. The valve seats have enough material in them to be opened up to take the larger A14/A15 valves. So why wouldn't you? They do still pop up from time to time. A bloke I knows brother bought three heads for $200, and one of them was a GX! I picked one up for $20, but it has a small crack in it. Which is odd, because when I had it hardness tested the guy said it was harder than a brand new falcon head. I would have thought if it'd been cooked it would have gone soft...... (Unless I cooked it?)