drmini in aust wrote:
Second digit was dropped from my `70 `Matic, it is YA2S5 13**
the same prefix was on my 1969 matic, since sold.
All the compliance plates I've seen on 70-71 roundys had the 2nd digit dropped.
My K book is PUB 1038 (final), whatever that means...
Inside cover actually says:
Morris Mini K RHD [vacant space]
Morris " " " LHD YMG2S4-L
Austin " " " RHD YAG2S4
Austin " " " LHD YAG2S4-L
Engine prefix [common] is 10YJ/U/H
So says the book, but Leyland have been wrong before. Look at the errors in their `black book' workshop manual.

The only PUB 1038's I've seen have Final as their version, and you are right about the errors in many BMC publications. For example, the parts catalogue for the Mk II series PUB1056M doesn't even mention an alternator, just a generator.
Mini King's catalogue says YAG2S4 for a Morris Mini K van, and YG2S1 for a Morris Mini K Sedan. 10YCTAH engine prefix for the Sedan and 10YJUH for the Van. Your Matic prefix of YA2S5 isn't listed in John's book.
Back to the original question, if the 'boat' has body prefix YG2S4 and the angled brace it looks like a MK II S body to me. I wonder if there's a hole for the fuel pump breather under the back seat? If it is a MK II S that should make it a bit quicker in the water, yeah?
Don't you just love BMC and their attention to detail in their various publications? Clearly didn't spend much money on Quality Management System consulting! I have all the Australian Mini parts books in my collection and you can see where updates to parts in a particular book are simply lost in the next version.