What a bike, my dad would also approve of that. He only owned pre Japanese bikes in his riding time but absolutely loved these Honda Four when they came out. Went to a lot of bike racing when I was younger and we always walked around the spectator parking to see what was there.
Your dad's bike looks a little like Triumph of 1930s with forks and rear frame, footpeg geometry etc. Looks similar to early twins in frame layout but seems to be a single cylinder as I can't see clear detail.
