My '75 K25 had the tripod mirrors as stock. There were three holes drilled in the sheet metal and they were installed with nuts and bolts. I was not doing any towing, so when I had some body work done I asked them to fill the holes and I swapped to the newer style of mirror.
The old mirrors worked great, but got in the way more because the tripod doesn't swing back flat to the side of the body. It always sticks out, even if you rotate the mirror head back in.
Bruce