The battery box frame is back in my hands again, and it looks fairly good.

I still have to attach the front piece. That is a job for tomorrow, as is final adjustment of the hold down bolts. In the photos you can see I have held one set of bolts in place with sticky tape for now. That probably wouldn't be sufficient for real use, so I better put nuts on too
The hold down plate actually fits, yay! I made it while the frame was still at the sheet metal shop being folded, and was sweating on getting it back to see if I had wasted my time. As it turns out............I hadn't.

I really wanted rivets, but besides the fact I couldn't find any, I also wouldn't fancy my chances of inserting them without making a fair bollocks of the job.

So I settled for these hex head bolts. I will rough the keyway up a little once tightened in place, and they will get a dollop of body filler in the holes. Sanding the filler correctly should give the appearance of rivets!
Had a disappointing discussion with the local battery shop staff regarding finding a correct style battery. No joy there. They have recently taken over the business and don't know anywhere I could get what I wanted. I did find the name of a place in Vic. that may be of help. I'll phone them in the morning.
With it looking unlikely that I will get exactly what I want, and bearing in mind I may run 12v anyway, I came up with a slightly lateral idea. The battery only needs to look original from the top and front. Assuming I eventually find ANY old Ford battery as a pattern, I can make a 'fake' battery top that is actually part of the battery hold down plate! If I make another plate that is slightly higher side profile, I can have the fake battery top showing on outside, with the real battery top hidden beneath, completely out of view. It's shifty but it should work if done well. May be able to incorporate the fake battery front into the mix as well.
All this just because I don't like the look of modern batteries.