Post a picture of what you have. Easy option tends to be to find a suitable motor and rip the totating bits out of that then wind your own coils and make the bearings and brushes to suit. That is how the Alyn one is done using a Lucus starter motor.

Do you have any idea of it’s perantage as to whether it was a commercial kit or just a spare set soemone ran off. The like sof Stevens Model Dockyard used to sell castings as well as several other sources.

I think I have some more details of this one that could be scaled up if that is the style you have

Or bigger. I think we need to see the castings first as if it were an enclose circular type a bit like the Stuart then you can just put the whole can and magnets in. If more like the one I showed above then you would most likely want to wind your own so the can and magnets don’t get used and you just use the smaller diameter rotating parts and would therefore have room to base it on a larger motor

That is certainly a big one and I do not recognise it as a published design. Maybe a home casting scaled up from a commercial one like the P M Research Dynamo.

If it were me I would work out what the main casting can be bored out to and what the likely lengths are going to be and then track down a suitable permanent magnet motor. Cut the ends off the case and fit that inside the main casting. Then make up suitable bearings for each end and a set of brushes.

Much like I did in this thread just larger. I’ll take a photo later of another motor I have that is intended for a larger version

I’ve a feeling it will want soemthing with a can diameter of about 3″