Where Exactly should the build sheet be?
All bases covered for the build sheet, but you can get the build card directly from Chrysler, (aka IBM punchcard). They keep records up to 1967.
The build card was used to make the build sheet and the fender tag, and is apparently the most accurate.
Send them $45 and proof of ownership, VIN,etc.
They will send the build card and a letter.
Here is the website, and an example of the build card (if you get it and need help with the codes let me know):
http://www.chryslerheritage.com/pg904.htm