I agree completely with Golden Boy's recommendations for vintage long cage derailleurs, provided the objective is to restore/retrofit the bike with something period correct. My recommendation for the Altus was based entirely on the assumption that you wanted to swap in something inexpensive and dependable so you can ride the bike. With those guidelines I stand by my suggestion. The Deore would be a waste of money in either case, for different reasons. A waste for resto purposes because it would look out of place. A waste for just making it dependable because the Altus is all of that. As a bonus, the Altus would play nicely with your original shifters. The only change you might want to make for trouble-free shifting is a chain with one or two more links, to make up for the big lower wheel on the Altus. I consider the chain a consumable anyway, depending on measured stretch and condition.