You may find it simpler to go by what is readily(?) accessible. Here you will find a listing of the 400MHz iMacs. Unless the video systems differ widely, the PAV boards may be expected to be readily interchangeable. The MLBs have little reason to differ widely, one might suppose. If you can find the parts you want with identical type numbers from other 400MHz iMacs, you should be safe enough to try the swapping.
In the swaps that you have already made you should have eliminated poor connectors/connections as the cause, but what of adventitious effects such as external EMFs, which can produce the colour effects that you noted, if not necessarily the same effects on geometry? Did you start up the mixed'n'matched iMacs in exactly the same location with exactly the same orientation? Or did you find the same behaviours in completely different locations? Were you careful to reset the PMU in each case, and ensure that the PRAM battery, which powers the PMU, was 3.3V or more? The PMU has to be reset carefully, or the battery life goes from years to days in a trice. The PMU is a computer-within-a-computer, with effects on much of what goes on in an iMac.
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In the swaps that you have already made you should have eliminated poor connectors/connections as the cause, but what of adventitious effects such as external EMFs, which can produce the colour effects that you noted, if not necessarily the same effects on geometry? Did you start up the mixed'n'matched iMacs in exactly the same location with exactly the same orientation? Or did you find the same behaviours in completely different locations? Were you careful to reset the PMU in each case, and ensure that the PRAM battery, which powers the PMU, was 3.3V or more? The PMU has to be reset carefully, or the battery life goes from years to days in a trice. The PMU is a computer-within-a-computer, with effects on much of what goes on in an iMac.
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