well, from the engine cover, it looks like it says Kawasaki. from the kick start and the shape of the seat i would say maybe 1970-1980? but from the holes in the brakes, early 80's?
LOOKS like v-twin, but i can't see it that well. from the rear disc brake, i could probably say it also has at least another disc brake up front. also has dual exhaust.
this is similar: http://motorbike-search-engine.co.uk/classic_bikes/z440.jpg
this has the kick start but no holes in the brakes: http://motorbike-search-engine.co.uk/classic_bikes/kawaskaki-kz750.jpg
heres the KZ1000 it looks A LOT like it!!!!!!!!!!!!!!!
http://lh4.ggpht.com/_6GoJc5g4Tqc/RiejbuomovI/AAAAAAAAAK4/B-UjxTpRjHU/DSC01800.JPG
http://www.gogocycles.com/images/1980-kawasaki-kz1000-g-for-sale-21331336.jpg
http://www.tristatecyclesales.com/images/vehicles/DC306A81-B470-A42C-AF832A557DDA152D.jpg
http://www.twowheelforum.com/photopost/direct_data/551/medium/sweet.jpg
http://michaelsmotorcycles.com/1977KAWASAKIKZ1000LTD807/2sell_047.jpg
http://www.artedelstein.com/OldBikes/78KZ1000/78KZ1000_Images/Image43.jpg
yeah dude i REALLY think its a KZ1000-KZ1200. compare with the artedelstein.com one's seat and rear shocks EXACTLY in the same place. same speedos, same foot peddle position above the exhaust, same rear blinker position etc. its not a perfect match because your dad had a different year of that model, also he could have moded it a little, and you can do more research on what year he had.
took about 30 minutes of research :)
cheers brotha! i hope you find that bike! btw nice hair!
lol they use the same rear wheel adjusters as my ke100 haha! thats awesome...