Gene Green asked:
"Looking at the equipment diagram for ERIE box cars 71800-71999 (renumbered from 92500-92699 in 1936 & 1937) these cars seem to have started life in 1919 as USRA single-sheathed box cars which were upgraded with AB brakes in 1936 and 1937.
Apparently they were also given steel sides in place of the original wood sides. Can someone tell me when?"
1936, and the cars received Climax radial roofs in the process. See Cullotta & Kline's The Postwar Freight Car Fleet, p 30-31 for more information plus a photo.
"Would either Tichy 4028 or 4032 be the best jumping off point to model this car?"
The rebuilds retained the original truss, so 4032 is out. If you want to go with Tichy 4028, you'll need to sand down the wood sheathing details between the truss members (which would be a chore), and replace the kit roof with a Climax radial roof. Another possible starting point is Westerfield 3365, the modernized N&W USRA SS boxcar with radial roof, but you'd have to check to see how close the N&W roof is to a Climax radial roof. It would be closer to fill in the scribed sheathing of the Westerfield kit than to sand down the details on the Tichy kit.
"My stash of decals includes nothing for the ERIE. Couldn't find anything suitable on Microscale's site. Is the Champ HN-63 the closest decal or have I missed something somewhere?"
Al Westerfield still sells his decals for the Erie USRA SS boxcars (kit #3314) separately. They're intended for the cars before their rebuilding in 1936, so you might have to come up with bits and pieces to letter your model accurately for your modeling period.