Nice example, likely dating from 1970 or so. Initial asking price of $3,500 may be on the expensive side given just the one RT pickup. It's also hard to tell if the case is truly an original Dan Armstrong case, in which case the accessory pocket is missing, or just a period hardshell case.
"For sale is this Ampeg Dan Armstrong vintage guitar, made in 1970. This guitar is USED and shows some wear, but is in overall very good shape for its age. It has been pro-setup and is ready to go. It comes with the original hard shell case. Feel free to ask questions, or call us for an in-hand description at 718-218-8201."