Well I stripped the oil primer and had to remove the plunger from the brass tube, clean it all up and as suggested I simply reversed the plunger so that it was back to original specifications and not with all the wear on it. I tinned the end of the brass tube and sweated it back in place without having to remove the outter casing by heating it up through the bottom where the check valve should have been. I welded the plunger back into the cap then made a new gasket to fit between the body and hopper. My brass tube was still there so I made it to the new length as it was a bit too long, tinned it and again heated the brass tube and soldered it back into the body. Some silicone and then bolted it back into place.
I did a test on the bench by putting some oil in the case with the plunger installed and sitting down. No oil came out. I started lifting the cap up and down and it started pumping oil out so it is a win. It is amazing how much oil it displaces each pump.

That is a good thought but are they a sucking or blowing fan?

Cheers, look forward to seeing how it all works out for you.

The crank handle supplied here is reversible. Lift the spring loaded pawl up and turn it the opposite way which can catch many people out. Engines are normally identified definately if CCW direction by letters at the end of the engine / serial number.
NO offense taken about your comments, they are valid and if we all dont ask questions we dont learn. Now with engine trouble shooting it is a question I often ask especially if it is exhausting out the air intake when running. Some time ago many people were troubleshooting this problem and we all wrongly assumed that it was a CW rotation and it wasn't until after a couple of weeks of ideas to try that a picture showed the CCW on the engine number.
Once that was identified and the pawl in the crank handle facing the right way the engine ticked over perfectly.

G'Day Andrew and welcome to the fun.
Try a Google search for a workshop manual for your model engine, sometimes they just turn up and your a winner. Sounds as if the pitting is above the top compression ring at TDC so no need to re-bore. If that is where the pitting is then hone it and fit a new set of STD rings and your good to go.
If no luck with the manual for your twin then a single cylinder will have to do but you would think there is one out there that suits yours.

Ok, the simplest way of confirming te direction is to remove the rocker cover and rotate the engine in the direction your handle allows you to do. From compression you have exhaust open  and close then inlet then TDC compression. If it is happing back to front then you know for certain.
As for that marine centre obviously doesn't want your business and you are probably better off with out dealing with someone so arrogant.
There are many canals over there from my aging memory and no doubt just as many marinas to visit. Also every other narrow boat owner you bump into ask them and tell them you are new to this life and are asking their advise. I think you will be very surprised at how quickly people then open up their knowledge and contacts. Plus by asking for their advise it makes them feel important, which they are and more likely to help.
Like with  our engine and tractor club members we all help each other where possible. I would not mind another week on a narrow boat again but it's half way around the world to get back to.

G'Day and welcome to the forum.
Nice little engine and should be good once it is running. Yes most diesel engine can run backwards but never recommended so first we have to establish the correct rotation of the engine. I say this because your starter handle has the ability to be reversed by lifting the pawl and rotating it around for reverse rotation.
Is there any letters on the engine serial number?
Workshop manual can be found by using Google search and they are free so this may also help you out with this engine.
As for the adapter some of the marine centres or looking online should score you the part you need.

Remind not to come to your place for dinner.