[Excaliber]

That variable venturi carb is in fact your worst nightmare, it was junk. That means a new intake manifold as well.

The heads are "drilled" for the fresh air jinjection ports fed from the "smog pump". That disrupts the exhaust flow so some welding/porting, and removal of the "air injection" tubes will need to be done.

Throw away the cam (need a new one anyway) and lifters.

Save the pistons, crank and rods? Maybe, maybe not, machinist will know if it's even worth while.

What you REALLY need to ask is:
Did the "police special" REALLY have anything "that special" about the block\pistons\crank in the first place?

The original cam would be a little more agressive than a "standard" application, (but you getting a new one anyway). The water pump could have been "bigger" (but your getting a new one anyway). The variable carb might have been a little bigger (but your getting a new one anyway). The exhaust manifold is likely "bigger" than standard (but your using headers anyway). The compression ratio MIGHT be a little better than "standard", but quite possibly to "low" to amount to anything anyway.

Oh I know!!! The crank might be an excellent piece, forged??? The block? Hmmm,,,hard to imagine it's anything much better than "standard".

I'm not sure a "police" engine makes any difference over a "standard" engine when a "re-build" is going to be done anyway.

What you got is a: 1989 351W "block" that MIGHT be worth rebuilding. Why would a 1970's block be any better or worse?
I wouldn't be swayed into paying more (or less) just "because" it's a "police special",,,,,big whoop.

Ernie