Hi Bill,
I've had NOS batteries last maybe 3 years before failing. I have one dead R59 that's in the shed and was wondering along your lines about replacing the internals. I also have a new NOS R59 in the box with the wax plugs still installed I bought in the early 80's that I am holding on to, for what reason I can't figure out. But, I don't want to break the wax seals and add acid only to get a few years out of that. Then, I thought of hauling an empty R59 to a show and swapping it out with one that is used to drive the car but I worry about the eventual chipping or marring of the paint under the support bar bolt heads from swapping it. The R59 repro tops look like a great alternative except for the replacement sides not having the correct pattern.
Decisions....decisions.....*sigh*

What I may wind up doing is this; bring a dead, empty R59 to a show and having more than one right side support bracket on hand to address the eventual bolt marring of the paint, swap out the battery. This would only be for a show I will be spending the whole day at.
Mike