Morris Minor Owners Club

That's interesting...it may apply to factory reconned engines but
does not apply to the ORIGINAL engines as my two certainly
had the plates on with '1100' on them.

Thats right Willie and the 1098cc & 1275cc Midget engines are also fitted with a small plate although it probably doesnt take much to remove them I expect.

My saloon's Goldseal engine probably did have the 1100 plate but no longer present. The red arrow points to a rivet where the plate was originally located. Maybe removed when factory reconditioned?
Re the engine number, the 8G162 might be a part number similar to those cast onto cylinder covers (12Gxxx) and along with the ES6013 made up the full engine identification.

I have a 'mystery' engine too; RKM 1121E 98586. Looks like a reconditioned one to me.

It turns out that the prefix 8G denotes a gold seal factory reconn'ed
Minor engine and the 8G applies to ALL sizes of these engines.

Plus the "B" series have 84G and the "C"series 86G. The numbers/letters after this denote machining sizes and a factory job code.

Re: my Mystery Engine (RKM 1121E 98586) I've also noticed, whilst trying to use a strobe for adjusting the timing, that the timing marks in my engine are attached BELOW the crank pulley, and therefore impossible to see because the front crossmember is in the way. All other A-Series engines I have seen have had them above the crank pulley. Perhaps these Mystery Engines are from a non-Minor?

Might be an odd suggestion, and I don't know the validity of the Idea. But could it perhaps be a mini (or other transverse car) engine that someone has mucked about with and fitted a rwd box?

Probabally a silly, silly idea

Could be. It's definitely not the original engine as it was a reconditioned unit judging by the fresh green paint and general very good condition of it. It does have the 1100 tag on it as well. Another thing; it has a spin-on oil filter, which could have been added, or maybe was there already. In which case, it could well be from a Mini. Are there any other differences (apart from the gearbox) between transverse and in-line A-Series engines?

The crank is obviously different at the drive end - and so also is the rear main bearing cap seal - essentially Minis don't have one - the sump is integral with the gearbox.

that the timing marks in my engine are attached BELOW the crank pulley, and therefore impossible to see because the front crossmember is in the way

And there was me thinking all A-series minors are like that! It involves getting your head under the car wlist trying not to cut your throat on the bottom of the number plate and looking up in the gap between the sump and the cross member.
If the car is on wheel ramps you can at least avoid the fight with the numberplate.