I have an old lugged steel Puch that has a high bottom bracket and seems to have a good track frame geometry (although it was originally a 70s road bike). Can I take out the simi-horizontal dropouts and braze in new horizontal dropouts to make a track frame?
The chainstay/dropout is "higher" (vertical distance) on a horizontal dropout vs. the track dropout.
If you just chop the old bit off, slot the seatstay/chainstay ends and insert the track dropout, you will lower the BB and create a sloping (rearward) toptube, and this will effect the geometry.
You will have to do some cold bending on the chainstays (downward) to get the correct lineup (rear axle/BB/front axle). You could always make your own track dropout with a lower adjustment slot, and tailor it specifically to the old frame.