In my enthusiasm to take it apart, I forgot to take a "before" picture, but here's a similar example fitted with a scope:

Here it is broken down:

Trigger detail, a much cruder affair than the original 160 trigger and the return spring pushes directly on the stock. Clearly veterinarians are not as picky as target shooters. Note the two grooves on the hammer that allow for a high/low power setting to be selected:

Valve body and stem detail, in spite of the relatively massive 0.5" bore the transfer port is a mere 5/32" diameter, presumably unchanged from the original 160 valve. The barrel is also rifled, with 8 shallow right hand grooves, which is unusual given that tranquilizer darts are usually drag stabilized.

Barrel markings identifying it as a "Red's Special", presumably an older variation of the one currently being sold as a "Long Range Rifle Type Projector". I believe the current version is made for a single CO2 cartridge, while the one I have takes two.

I'm not sure if I should reseal it and keep it as is, or redo the internals to turn it into a big bore PCP. Decisions decisions...
edit: The manufacturer replied to my query about its date of manufacture and it seems that it was manufactured in the 70s, so I will most likely not be modifying it.