It is a Mark 1 dial, commonly referred to as a floating dial because the word cosmograph appears to be floating. The Mark 2 dial was reduced to 4 lines of text with no gap. They only appeared in the first batches of watches in 1988 and are R serial numbers in the main and are extremely rare.
Even rarer still are the Mark 1 white dials with black Sub dial rings, which from my studies appear to have the porcelain dial.
I wrote a fairly comprehensive piece on these dials a few months back.
http://forum.tz-uk.com/showthread.ph...-Final-Outcome