If it's welded and blended in correctly you won't be able to tell.
As regards the puches do searches, there are a lot of companies make these.
With regard to using, no holes needed, whatever it touches with enough pressure when set up in a fly press it will form to that shape, metal forms very easy to different shapes.
If you have any car restorers that do old cars in your area these would be a good bet to approach, as they are likely to have a fly press.
The actual depth of the punch is controlled by the depth set on the flypress, so will take a while to get first one right till you're happy with depth, lock at that and then punch away, set it too deep though and instead of punching the shape you want will pas all the way through the die and make a complete hole!!
I will dig out the details of where I buy mine from later and post it up.
tabetha