Clark Propst asked:
"I have a Tichy undec single sheathed box car. Would it work for a Pennsy X26? If I change the doors?"
Yes, with the caveat that most Class X26 boxcars received minor rebuilds in the mid-1930s, giving the cars Hutchins roofs, truss reinforcements as necessary, and steel replacement doors in most cases. Some cars escaped this rebuilding and continued in service with the original Murphy XLA roofs through the 1940s.
"If so, are decals available?"
You might have to do some digging. Good sets include C-D-S 310, Westerfield D3306, and the Speedwitch PRR CK boxcar set D116.
"Nah, I may do it Milwaukee. I think I have enough leftover Westerfield stock car decals to letter it."
MILW is a good choice - they received the second-largest allocation of these cars (4,000 cars; PRR received the largest number with 9,900 cars). Westerfield also offered these decals separately.