Thank you everyone for insight. I appear to have matching numbers cars, using traditional number plate/engine block/head and certificate determination. These type was purchased from original owner.
I’ve owned many xk120s xk140s and xk150S.
Most of them, including my E type had letters stamped into the spark plug valley. My xk140 has a “C” my 150S has an “N”, my e type has and “A”.
What’s confusing is that I’ve seen a few X150S s with an “A” , and several e types with an “N”! Bloody confusing - and so far no real explanation about what N and A signify.
The rear plinth plate seems to be a foundry number - without any chronology associated with it - but No one knows for sure about that either - correct?
Anyone have more insight?
Let’s be sure we are using a universally agreed terminology. Stamped means the character was done with a hand tool and a hammer. The hammer whacks the tool which digs in to the metal and leaves an indented character.
On my C-Type head the letter C is not stamped, it is molded during the casting process when the liquid aluminum was poured into a mold. It is raised above the level of the surrounding metal.
If your N and A are raised molded, I would like to see pictures, as I have never seen these.
If they are hand stamped, it relates to the foundry production date, and also to the type of head. A straight port head with a stamped letter A could very well have been made after a B-type head with a stamped letter N.
Let us know these letter/number stamps as well as the serial numbers stamped at the front, and we can add them to the ongoing database and maybe eventually figure out whether or not there is a discernible logical sequence.