Special Order 360?

Oh, guess the "?" In the title wasn't enough of an indication that I was asking, I mean of course then you could have read what I wrote and seen that I was trying to get information...

Smh , anyhow the car itself I believe to have been originally a 318 car based on the VIN, it did have air conditioning and power steering which that was gone as far as the AC goes, the k frame with the power steering set up and the pump was still there which I may wind up using...
The hood is shot rusted out just past the hinge on the driver side, inner fenders do need some love but they give me what I need to put my " Duster" back together, bought it just for the frame rails and the front radiator support...
And yes, found out that the heads are not anything special there was a broken head from a boat under the intake but after the heads came off the motor turned freely.. found a broken exhaust valve with a chip out of it so, looks like it's getting stroked & bored with a set of aluminum heads and an aluminum four barrel intake, my baby blue 72 is going to haul the mail!
Question, why would you use used frame rails and radiator support when they are available new?