From what I can determine, the physical dimensions are the same in either case. However, the internal gearing is most probably different. The planetary gear set output shaft has a ratio or either 1.82:1 or 1.76:1 depending on engine application (lower torque vs. higher torque).
Following link is an online copy of a 1971 Chevy transmission manual which discusses the operation of both the Powerglide and the TH500. See page 6. http://www.tocmp.com/manuals/trans/TTransChev1971/TTransChev1971.html