Spindle/brake rotor hub size -- how do you tell?

[got2haul]

Please forgive my ignorance:

I want to change the brake rotors on my 1980 1/2 ton.  It has the stock spindle.  One option it has is heavy duty power brakes.  It is not a "Big 10" model.  How can I tell which size the spindle is?  When you purchase new brake rotors, do they come with lugs already pressed in?  What about the wheel bearings, seals, etc. -- do those normally come installed in the new rotors?  (I assume it's all one unit, rather than a hat/hub setup) or does all that have to be purchased/installed separately?

[zieg85]

My experience is with a 1986 so hopefully it is the same.  There is a visual difference in the thickness of the rotor and calipers.  I think everything else is the same.  All the rotors I have bought do come with studs but not bearings or seals.  I am sure if I am mistaken it will be pointed out.  My $.02

[VileZambonie]

Measure the thickness of the rotor. If you have a micrometer or dial caliper/digital caliper etc.. or even a ruler. The difference is the rotor thickness. Approx 1" for light duty 1.25" for heavy duty

Also it does come with lugs but not wheel bearings or grease seals or grease