I have an 87 N/A that has a bad coolant seal, it's been sitting for 3-5 years
I've ran it and drove it up the street and back, it runs good but likes to idle at 12-1300rpm
If I adjust it lower it drops to like 500 then dies.
When I first got it I ran prestone coolant flush through it cause I found white chunky stuff floating in the radiator and thought it might be clogged then I flushed it out real well with a garden hose and refilled with distilled water. I've since drained it and filled with 50/50
If I turn it over then pull the plugs out there dripping wet with coolant
Just a couple days ago I pulled the top filler cap off and found a piece of orange rubber about 1/4 the size of a sunflower kernel, Which I believed is a piece of the coolant seal?
My question is if it's been sitting for this amount of time is there gonna be water damage that would prevent any part of it from being rebuildable?

 

Probably.
The irons have small grooves that the soft (coolant) seal grooves set it. Water/coolant from a failed seal is allowed to enter those grooves. Left long enough, that will cause pitting and corrosion to the point that the irons are unusable.
3 to 5 years is certainly long enough.

 

After 5 years from sitting with a bad coolant seal, I'm surprised you were able to rotate the engine! Normally rust locks everything in place and turns the engine into a boat anchor.

 

When I got it there wasn't much in the cooling system but this is what was in there
It still runs great and starts right up