Hey,

I can't tell you much about your Siffert, but maybe add, that my Pre-Viceroy also starts it's serial with 204XXX and has a 11i as movement. As far as I understood, the different watch types (T, MH, V) were produced in batches like you can see here: http://www.onthedash.com/Guide/Master_Reference.php4 . A Mark 6 Siffert should be a 224xxx, 241xxx, 242xxx or 243xxx.
Sorry, more question marks than answers now I guess ;) ,

Nico

: Thank you for your comments gentlemen!

: The serialnumber starts with 204, and the movement is indeed a cal
: 11. I do not have good pictures of the movement, only this which
: I got from the seller. I bought it from a watchmaker who had it
: sitting in a drawer for years. The dial and hands are in very
: good condition, and the lume still works!

:
:

: Stian