I am surprised that KHI never developed their own unique font / style of stamp?
I basically is just 1/4" standard industrial stamping. I'm sure the factory had a machine type press of some sort?
I had this set of stamps for 40 years. It fell into my lunch box one day by accident at the large commercial printing plant I worked at for 34 years!
But years ago, I would put some time into doing a frame # job I would tack weld a bracket to frame depending how many digits were used. Put 1 stamp in, fill the rest with lower spacers real tight and snug. Then just go 1 at a time replacing spacers with a stamp
You had to hit it once hard, but then with the convex radius of the frame neck you could lightly rapid tap it a little more to the top or bottom side by rocking it a little, had to get the feel of it.
Then of course a little rasp or file action, some primer before paint.
Just for the record, we never dealt in anything that was stolen, just old titles from wrecked bikes or bikes turned into drag bikes that a title was just sitting in a drawer not used. So if another guy needed it. Here is a quick pic of what I have. Have the whole alphabet & #'s