The logic of buying a ready to run crate motor vs. rebuilding a "yard" motor is a matter of balancing time and money.

Digging around to find a suitable "yard" motor is time consuming and in many cases a risky aquisition. Then factor in the time to tear down and the cost to re-machine, cost of new parts, and the time or cost to reassemble against getting a ready to run new or rebuilt engine off the shelf.

If we are talking a short block or custom built to spec ready to run crate motors vs the above "Yard" motor rebuild I don't think it is to hard to see the logic in leaning towards new vs old at similar cost - but the final cost does depend upon what you are trying to do.

If you are looking for a 4 bolt bottom end with new crank, rods, pistons, etc., a new crate short block is hard to beat. If all you are going to do is freshen up stock parts then a yard motor may be the way to go. Start talking a stroker and the machining cost of a stock yard block for clearancing appear to exceed the cost of a ready to use crate motor.

And then rebuild and port Yard heads vs. a pair of new ready to run Vortec's for 500.00?

Maybe if you can do the machining work yourself and have the time - but for me starting with a new short block and then bolting on new parts from there is working out to be the most cost effective.