August 2004 Mainline Modeler has an article and plan on the X-29.
Here are some internet shots for you:
http://www.steamfreightcars.com/gallery/boxauto/prrx29.html
Dave Nelson
PENNSYLVANIA
124600 EW 8 11
EH 12 6
CAPY 100000 IL 40 6
LD LMT 124600 IW 8 9
LT WT 44400 P57 11 41 IH 8 7
CU FT 3042
BLT 11 32 X 29
The palcement isn't quite right and on the line w/ the BLT date the X 29 lettering is about twice the size as the rest and lines up at the bottom. Depending on the era you want to represent you might want to change the year on the rewiegh date (on the line w/ LT WT) from 41 to whatever. Hope this gives you what you need