This little gem arrived today, an EBay catch and it's looking good so far.

Watchbase tells me it's a Speedmaster MkII (I knew that bit) MD 145.034 and is gold plated.

https://watchbase.com/omega/speedmaster/md-145-034
from which I quote

"The Speedmaster Mark II was the first departure from the classic Speedmaster (Professional) design, which at the time of introduction (1969) had more or less reached its final stage. It is said to be intented to replace the classic Professional, although this never actually happened.

The Speedmaster Professional Mark II MD 145.0034 as pictured here has a stainless steel case and matching bracelet, both gold plated. The glass has a black tachymeter ring; it is not entirely sure whether this is the original configuration, as most have it in maroon. The radial alignment of the numerals on the subdials and the applied indexes are notable changes over the stainless steel versions."
I'm pretty certain that the bracelet, Omega signed clasp and all, is not original but is a pretty fair match, colour-wise. I think gold bracelet suits the watch well, don't you?
Now about the matching medallion & chain......