At 07:45 PM 11/14/04 -0700, Dougal Oliver wrote:
>"Is anything usually stamped on the engine block under the riveted plate that shows the engine number."

No, absolutely nothing. It should be a plain smooth surface.

>"I am looking at a car that I am told has the original engine but the plate is gone. Stamped on the block in this position is 16 G U #######. "

Since it was not put there by the factory, it is not legal proof of anything, technically totally invalid. However, it may be pretty good circumstantial evidence of being the correct original number. If someone wanted to falsify an engine number, it is very easy to make a new number plate of the original type with any number desired. The fact that it is stamped in the casting is fair indication that someone wanted to preserve the original number forever.

This might be done as the best alternative if one does not have negative impression stamps handy to produce the original type raised letters in the original type plate (or does not have an original type plate handy). It is fairly common for the original plate to be lost or destroyed in acid bath when cleaning the part during machining. A lot of people do not realize that the aluminum plate will be destroyed during the hot tank cleaning process, or may otherwise simply forget to remove the plate before hot tanking. It would be nice if it was replaced with an original type tag, but stamping the number in the casitng may be just as valid.

In any case, since this removeable tag is the only mark of the original engine number, it is difficult to prove that it is correct even when it is perfectly original and has never been removed from the engine. That's just the way things were done in the time when the car was manufactured. Best evidence in current day would be if the engine has normal wear for the expected mileage, and has never been re-machined, and is still in the car with all original numbers. But even then it would still be hard to prove that someone didn't switch engines in a past life, and switch tags to keep the original tag with the replacement engine. This is why in more recent times it has become a legal requirement that the number must be stamped in the casting at the factory.

In the real world we have to work with what we have at hand, so we do the best with what is presented to us. If the engine has oversize pistons or sleeves, that would show that it has been machined for repair or rebuild, in which case the stamped number might be accepted as original, unless there was some other evidence to the contrary. If the engine appears to have original wear and no rework, then one might be suspicious of fraud, such as intentionally mismarked replacement engine. But it's still not absolute proof either way without some additional supporting evidence.

So how important is it to you that this should absolutely be the original engine which was installed in the car at the factory, and why?

It is nice if there is no indication that it was previously stolen (not an illegal installation). For concours show purpose it might be nice if it was more certain to be the actual original engine, but even they it may not be absolutely necessary. For a nice show car or a daily driver, probably no one cares. If the engine is original type with all correct original features, and you install an original type tag on the engine with the correct number original to that car (or as close as best guess can provide), then for all practical reasons it will pass muster as the original engine (no other evidence to the contrary).

An engine might have any part replaced for a valid service repair. That replaced part might be a valve or a piston or even the engine block. Replacing any individual single part for repair does not necessarily make it a non-original engine, even if the part replaced was the cylinder block.

You should review these articles:
Identifying Numbers found on the MGA
Is it Legal to Buy or Sell a Title?

If none of this is certain enough to satisfy your personal demand for originality and for best proof, then you have to look for a different car, because that's as good as it gets. Before I might make any suggestion as to what you might what to do with this situation, I would ask again, what is your reason for concern?