Is it Diesel...or 'lectric?

I still have the jigs I used to build these. If these old stiff fingers let me, I'll show how I built them.
I didn't put springs on these because they were just for display. It wouldn't be a problem to do so.
 
For those who have old MRs (the only ones I ever read now), in the May '74 issue on page 37 is a very good article on making them that would be a good supplemental guide to a tutorial.