For any other novices to shaping metal in the group, I can't sing the praises of a tucking fork enough. A great tool. Sure the hammers worked fine but for me, not precise enough and the fork makes such a perfect tuck. I found I could make a tuck without flattening it and test fit to the buck to ensure I was going in the right direction with that particular tuck. Sure enough, it looked ok. At one point I made 3 tucks before flattening them out and test fit and I could see that they were exactly what was needed prior to flattening them out. So if you're thinking about metal shaping, make a tucking fork. It's well worth it. Saves a lot of hammer time.
I wondered what that tool was used for.
Then last night I was looking through an old Street Rodder magazine and saw one similar to the one you made.
Now I know.