Help identifying Spitfire engine

[lesnyd@bb1t.monsanto.com (Larry E. Snyder lesnyd@monsanto.com 314-694-3626)]

I've been suspicious of the drive train in my 1968 Spit Mk3, since the gearbox
has synchro in first, making it definitely a non-original box. So I took a
look at the number on my engine. Since it doesn't match anything in any of my
books, I kind of figure I got the number off the head, not the block.

Anyway, the number is FK6847HE (or close, failing memory, you know). I think I
remember the "H" as meaning high compression, but does anyone know about when
this head was made and what the other stuff stands for?

Thanks much,

Larry
lesnyd@monsanto.com