If you need one of those, I have a sealed mk5 listed as well. Comes with a nice Pilot.
Nice! And sorry for derailing this thread with the history of early SP first stages.
After realising some inconsistencies in what I wrote, I went back consulting the extensive collection of SP catalogues available here:
Looking at the catalogues in the period 1963-1980, we can see that originally in 1963 Scubapro was selling just two regs, both balanced, one is the (in)famous "J" model 7101 incorporating a mechanical reserve, the other is the "standard" model 7100, shown here:
This strange reg is already "balanced", as the text clearly explains, so it is basically the predecessor of Scubapro MK I.
The year later, 1964, we find already the three decreasing-quality regs:
mod. 7100 - Mark I - balanced
Mod. 7105 - Mark II - unbalanced
Mod. 7104 - Mark III - unbalanced, cheaper
They are shown here below in the same order:
In 1965, these 3 levels are unchanged, but a 4th level, even higher performances reg is added, model 7106 - the Mark V, shown here:
Please note that in this early version of the Mark V there is no rotating turret and there is only one, on-axis LP port.
No catalog is available for 1966, unfortunately.
In 1967 we find again the same 4 regs, ordered in decreasing performances as:
- mod. 105 - Mark V
- mod. 101 - Mark I (v2)
- mod. 102 - Mark II
- mod. 103 - Mark III
Whilst Mark II, III are unchanged, Mark I is now the new model, resembling closely the previous no-swivel Mark V of 1965, but more rounded, and is shown here:
The Mark V, on the other side, is now the commonly known version, with swivel turret and 2 LP ports, as shown here:
Back on topic: the Scubapro MK III is found also in subsequent versions of the SP catalogue, until 1980. The MK III is still present in the 1980 catalog,, so it was produced in years 1964-1980 (I do not have access to catalogues after 1980, so perhaps it remained in production further).
The MK I, instead, also remained in US version of the SP catalogue until 1978, for reappearing in 1980 re-marked as MK VIII. You can see it here:
The MK I-v2 (flow-through, lately renamed MK VIII) is a nice 1st stage, which can be used even today, instead the original MK1 was the one with severe problems, which Scubapro retired.
I apologize for the long post, and I hope to have clarified the glorious history of those early SP first stages, of which only the MK II survives as of today.