the inner workings are towards the middle, so your still left with the axles and housings to deal with. There are two completes running on ebay and a complete set of outrageously priced controls.
Depending on how much you are wanting to narrow it, you may be able to do it with stock parts. Do lots of research.
I've got one under my '32 (pic below) but it's an early ('35/'36?) unit with after marker spring hangers for a '32 spring which keeps the tires in under the fenders. If yours is the later '46-'48 wider unit, the right side Columbia outer housing bell will need to be shortened to match a shorter and earlier left side Ford bell. You also might want to replace the spring hanger forging on the Columbia bell to match the left side bell or use Pete and Jake spring hangers as I did. Every thing else from an earlier narrower rear end should work. If guys can convert Ford banjo setups to nine in. outer bearings and splined axles, this should be a no brainer.
Check with Hot Rod Works in ID - those guys narrow banjos and re-machine the axles (or convert to modern axles).
Thanks for the replies. The one I've found is a 1947. I wanted to make sure it could be narrowed to fit under a Model A before I invested in it. gary