C-10 and C-20 Frames the same? C-20 suspension on a C-10?

[Ziptar]

They got a 78 C20 3/4 Ton truck in the yard near me last week. I was looking it over and thought it might be nice to have the heavier suspension, axle, and 16.5 wheels on my truck.

Are the C10 and C20 frames the same? or are they heavier on the C-20. Can I just switch the suspension and rear axle over onto the c-10 frame or do I need to put my bad, cab, and front end on it?

Think the 3/4 Ton stuff weighs enough to change MPG much??