Thanks CC, Chuck and Arnold for your comments

I got a little more done today, somewhere inside both of these lumps of brass there are 4 crankwebs and a flywheel, my mission, should I choose to accept it, is to find them.

So I hacked off a length of the long bar and chucked it in the lathe, faced it and turned it down to 28mm. Then I centre drilled and then drilled through progressively to 4.9mm drills, then finished it off with a 5mm reamer. (I guess this was a little overkill but I thought is would result in a good fit for the crankshaft)
I then chucked a 4.5mm drill in the tailstock the wrong way around and just positioned it so that it just stuck into the hole in the brass bar. Then I parted off a 5mm section, and rather than it dropping into the swarf it just got caught on the backwards drill. Then repeat for the other crankwebs.

Then, after de-burring the parted off crank-webs, it was time to make another jig for drilling the holes for the big end pin and the little compression-hinging-hole-thingy. I made the jig as per the instructions in the plans. I drilled all the 2.5mm holes first, then using the pin to lock the disc I repositioned the x-axis and drilled all the 4mm holes.

And so I ended up with this,

You may notice that one of the crankwebs is not as good as the others. When parting off the carriage moved slightly, but it's not too bad ( a blind man on a galloping horse would never notice

) I think I might be able to salvage it.
Next I will be milling the crankwebs and also turning the flywheel.
Tim