My 1955 TBird was converted to a 12 volt electrical system before I bought it.  I have the engine out of the car.  I removed the battery tray to clean the frame and clutch linkage.  The battery tray has been modified (crudely) so a wider 12 volt battery will the 6 volt tray.  Can I swap in a battery tray from a 56 or 57 Bird to fix this problem or do I need a special 12 volt battery?

I noticed this post come up earlier and was just planning to make a new tray for my TBird at the time that would suit a conventional shape battery. Years ago I went through the process of trying to buy a battery over here to fit but never found the correct size and ended up putting some MDF in the tray and having a conventional shape battery sit on top. I started making a battery tray earlier this year but didn't say anything until I had made some progress.
Here are some pics of what I have done so far.



Version 1 and 2 trays.


 






It has been lots of trial and error but I am now happy with the results. I was originally going to use mild steel but decided to use 316 stainless instead. The stainless has been much harder to work with but I think it was worth it. I probably over engineered it a bit as it has come out heavier than the original. The tray is 1.5mm, mounting brackets are 2mm and the heatshield bracket is 3mm so that it had a few turns of thread in it rather than welding nuts on the back like the original. What I didn't take into account are the mounting brackets which are much wider than the original so I could have gone to a thinner gauge steel to save some weight. Version 1 of the tray was 1.2mm thick more like the original but the 1.6mm on version 2 was much easier to TIG the corners. Still haven't worked out the heatshield yet.