easy to mount a tailpiece. there should be tons of videos showing this process.
find the centerline on your neck... your bridge and your lyre tailpiece. establish that line... it's key.
then position your tailpiece at the distance you want it from your bridge.... establish a 90...
those dean USA pickups are pretty freaking fantastic. I don't know about the Shenker models in specific... but generally... really good.
Does Dean make them in house? or do they contract their pickup winding out??
The stuff that dried clear and hard does NOT look like titebond. that looks more like hide glue. which would be. kind of surprising for 1987.
I'd put the question out on the les Paul forums.
As far as removal goes.... outside of epoxy or CA glue the answer is going to be steam and...