Found an old Max Grey (probably) S.P. oil tender on eBay for a "buy it now" price of $75 and took a chance. Turned out to be a *really* old max Grey tender, probably from the mid to late '50s, as it had only a generic brass turning to represent the brake cylinder, minimal detail elsewhere, twice-oversized rivets, and -get this- solid brass wheels with no plating whatsoever. On the other hand, all the basic dimensions were correct, and with the exception of the left rear stirrup step all the original parts were present and accounted for.
A trip through the old parts box yielded (A) a proper S.P. pressure style cap for the oil bunker, (B) an oil dipstick, (C) a marker light box for the tender deck, and, (D) an S.P. style water-cooler box for the bulkhead.
A call to Walthers revealed that -wonder of wonders- they actually had Cal-Scale tender brake sets and NWSL replacement wheelsets in stock, so those got ordered.
The missing left rear stirrup step presented more of a problem as nobody makes anything today that resembles the original, so I cut one out of an .065 brass sheet; using a jeweler's saw to cut it out, fine diamond-grit pattern-makers files to clean it up, and the right-hand rear stirrup-step as a template.
The original S.P. tenders had a series of three grab-irons on the face of the tender bulkhead so the engine crew could climb up on the deck at fuel and water stops, so I bent them from .015 steel guitar string that I favor over brass wire both for it's strength and for it's ability to withstand higher soldering temperatures without melting. I also used the same gauge of guitar string to make the fuel line that led from the fuel bunker to the locomotive, and for the brake rods.
The brake line on the rear of the tender I fashioned from a short length of .045 brass-wound guitar string that I use because of it's strength. (My locos get used a lot, and soft brass brake lines tend to get broken off in handling.)
Upon disassembling the tender I discovered there was a 2 ounce lead weight bolted to the frame (probably to ensure solid electrical contact with the unplated brass wheels they were using back then), so I removed it, washed everything in warm soapy water, and set up the resistance soldering rig while the tender parts dried out of doors.
After that, it was just a case of removing the old brake cylinder, soldering on all the new parts, installing the new wheels, and grit-blasting the entire thing to get rid of it's dark patina and provide a rough surface for the paint to adhere to. Grit-blasting a bit longer than usual also had the effect of eroding off a good portion of the previously oversized rivet detail. (They're all still there, but now they don't stick out like sore thumbs.)
With a minimal investment I now have a tender whose detail will more or less match a modern brass steam loco, or at least not stand out as being the rather crude representation of an S.P. tender that it was when it first left Japan, Lo those many years ago, and it made for a fun and somewhat challenging project as well.
-Pete