[blucar]

In 1974 I bought a very nice '57 Bird for my wife as an Xmas present, paid the princely sum of $3,500 for the car. The odometer showed 68k..
In about 20K the engine started to knock so I had the engine torn down to find the problem. As my luck would have it, the engine was not what it reputedly had been claimed to be by the man I bought the car from.
The engine was a 312 block with 292 heads, miss matched rods/pistons, a typical poorly overhauled engine in lieu of a rebuilt engine. Everything but the block was discarded. I found a set of ECZ heads, took them to the shop rebuilding the 312. The heads were rebuilt, valves, seats, guides, etc.
Shortly after the engine was reinstalled into the car coolant started to appear in the engine. Extensive testing revealed that several of the head bolt holes minute cracks around them on the valve spring/rocker arm side. The result of over torquing the bolts.
An extensive search could not produce a good, re-buildable set of ECZ heads. After a couple of months spent looking for ECZ heads I happened to remember a Y-Block that we had pulled out of a one of my company's '64 F350. The engine was a Ford rebuilt long block that had grenaded when the crank broke.
When we tore the discarded engine down we found that it had ECZ heads on it.. The Ford gods had smiled down on me. Lucky for me the Ford authorized re-builders were not above mixing parts...