Dad always favored rebuilding them with Sprague Orange Drop coupling capacitors.
That is because back in those days they were the only game in town. A lot has changed since then! There is no way I'd use orange drops for any kind of rebuild or repair at this point- they are simply outdated.
If you are selling a set of these amps I would leave them bone stock, don't do anything to them and let the buyer worry about that. Anything you do to them can damage the collector value, even though they may barely work because the filter capactors are shot.
OTOH if you do replace filter caps, the only way to do it is to do it so well that no-one can argue with the parts choice and workmanship.