Advice on buying junkyard engines?

My place has a core holding of 50’s-70’s cars/trucks. Anything newer gets dismantled and shredded. Some stuff they wait for it to get picked over if they know it will sell. They have over 5000 vehicles and there is never a shortage of stuff to go to the shredder and there is open space for more vehicles.

And get this, the most sought after part is computers for dodge trucks, they are sold as soon as they get them.

I was looking for a computer for my 5.9 swap and could never find one in the pick n' pull yards. I think they pre-pull 'em. Why is the demand so high on them?