Here you go, make it a 5 window cab.
http://www.autobodyspecialt.com/cgi-bin/commerce.cgi?preadd=action&key=C-1106JI hope I'm not coming off too critical. I have 2 54's myself, one for parts, one for building. My projest(s) aren't nearly as complete as your are.
My trucks already have an open driveline, my builder is a 3600 truck and the parts truck is a 3800.
I'm going to swap out my 3 speed for a 4 speed also. Mainly because my shift linkages are messed up. I've thought about a T5, heck I've even bought one. I think I'm going to hang on to it for future use though.