If it's a real Sandman leave it as original as possible. That's where the money is today and forever more.

If you have a desire to own a modified vehicle by a poverty pack and go to town where the intrinsic value isn't there.
The more you modify the Sandman the more value is lost. Where as, if you add power and comfort to a Belmont (etc) you are creating something with added desire and not the other way around.

This is all assuming that the Sandman isn't a basket case to start with.