I have an '81 750k with manufacture date of 4/81. I have single front disc (left side) and rear drum.
My wheels are spoked and a 4 into 2 exhaust (I don't think its stock because the chrome is crappy compared to the rest of the bike's chrome).
Here's a link I found giving the specs
http://www.bikez.com/motorcycles/honda_cb_750_k_1981.php. It say's dual front disc with rear drum. I think this info is faulty (or describes a European version) because they also say an 18" rear tire which on my bike is stamped as 17" on the manufacturer's plate and is what I have mounted on my rear rim. The photo doesn't look like my bike either. Handlebars, side covers, blinkers and rear light assembly are different.
So my answer is no, you can't trust what you find on any one internet site. Look around and find where your model fits. You may find like I did with the exhaust that someone has made some customizations to your bike. Ask the forum if you have specific questions. The answers may be illuminating.
Anyway, look at your manufacturer's plate on your steering column and see what it says. You might find something that says your bike is worth a ton of money or simply violates California's anti-pollution laws (^_^)
Jimbo
'81 Honda CB750K
'74 Moto Guzzi Eldorado (LAPD)
'08 Kawasaki Nomad 1600