Sixty years ago refurbs would be much of the work going on at any large railway works - taking engines apart, stripping them down to the chassis and reassembling almost a new one in their place. The ingenuity today's preservationists demonstrate in doing this without any of the facilities of a plant is truly a thing to behold.
(Source: some of my family restore steam engines. I once tried to drive one and I was terrible.)
Here's the process.[1] This had to be done every 120,000 miles or so, which is every 1-2 years. On top of that, there's a few hours a day of routine daily maintenance.[2]
I wish they'd do something a bit more streamlined like "Mallard"
See https://prrt1steamlocomotivetrust.org for more info on the new Pennsylvania T1 locomotive that's being built.
Me? I don't care. It's a nice thing and I enjoy seeing it in whatever form it may appear as. Personally I like the tender that has a corridor from the first coach through to the engine plate. That seems quite nice for the driver and fireman to have delivered more than just some eggs and bacon cooked on dirty shovel :)