Finding the correct 3″ COLO taillamp for an American Austin is never an easy task. There are some lights that look very similar, but they usually have the mounting studs in the wrong places. If you need something that looks very close and are willing to do some work to modify it, there is a Buick taillight that has the correct style spring retained taillight assembly. Besides having the word BUICK stamped in it rather than COLO, this lamp has a small opening at the top as well which you may want to close up for it to look more convincing on your Austin.
The Mounting holes appear to have the correct orientation, but you may wish to contact the seller to ensure the proper spacing.
Click here to see more: American Austin-esque Taillight Sold for: 85.00
If someone has a correct COLO photo they wouldn’t mind sharing, I can post it for comparison.