Actually the T-2570-B only carries through 1925 (small drum rear ends) and the T-2570-C covers 26 and 27. The -B part is only @ 3 1/2" long (going off of memory here, so be kind) and the -C part is more like twice that. I'm almost positive that the spring Dudley is hunting is actually the T-2570-C, but the only ones I could put my hands on today are modern reproductions which I don't think are cosmetically like the originals. I know the originals from our speedster project are here somewhere but I can't find them to save my life.
Dudley, do you know how far it is from the stud on the framerail to the back of the brake linkage where this spring hooks? The T-2570-C springs are around 6" long, but I didn't think to go out back today and look at my early chassis to see if that would be about right.
Editing to add a couple photos. Sorry they're not that good but it might help someone recognize what Dudley's hunting.
The spring in question can be seen just above the wiring harness clip on the framerail in the center of this photo:
Here's a better photo showing the location, but the spring appears to be a replacement (doesn't have the tapered ends with a separate piece for the hook):
The Model A part number is A-2492 but the parts price list states that it's the same part as a T-3054. It obviously ain't a valve spring, so the price list must have a typo.
One source I've seen states that this spring is 5" long which doesn't match up to any of the versions of the T rear brake shoe springs, so I'm not sure what to think. Wish I had a better photo to share...