Can't identify but HAVE restored many an item of similar sort.
The first thing I'd do is get access to the piston somehow and pour in some penetrating oil, seal it back up, and let it sit for a week or more, maybe several weeks, adding more oil occasionally as required. Then you have to make or get some sort of shaft to turn the crank. The penetrating oil (or old hydraulic or motor oil) breaks things loose MANY times. When it doesn't, we have used a trick on Allisons and other things with pistons in them many times that works.
We first remove the camshaft (I know this one doesnt have one) and rocker arms. Then we use a dead blow hammer to work the valves loose and make sure they are closed. The we took a spark plug, broke off the ceramic end, drilled it out, tapped it, and screwed in a quick disconnet such as you find on 2500 - 3500 psi water sprayers.
Then, you guessed it, connect the water sprayer and turn it on. Voila! It hydraulics the piston out. You DO need to cushion the place where the piston will come out to avoid damage, but we have "rescued" and returned to service over 25 Allisons that way. We used to use a grease gun to hydraulic it out, but that was REALLY dirty and messy when it came out or a valve let go in your face. After we tried water, we never went back.
So ... I'd apply the penetrating oil to the center valve and try to get it unscrewed, and then make up a hydraulic fitting that can connect to a sprayer. But ... I'd try to machine a hub for the crankshaft and try breaking it loose with oil first. You have to have some patience here since the object is to free it up without damaging anything.
There is a compay called Kano Labs here in the states that sells product called Kroil. Absolutely amazing what it can break free. You might try to google it and find some.
Good luck and let us all know how it comes out ...
LOOKS like an aircraft air pump, but so do a few things that really aren't related to aircraft.