These bodies have been discussed before but doing a search on C15A and Radio Body I'm not finding the posts which would be most helpful. Does anybody remember the tread? Bob you have posted pictures I think.
Here is a link to some pictures of the body type taken at the CMP 84 Symposium
http://www.canadianmilitarypattern.com/CMP84.htm look at pictures 26, 27, 35, 109, 231 and 232.
Plus information in Bill Gregg's and Bart Vanderveen's books.
If the box found is in good condition it would make a great unit for a C15A chassis
Cheers Phil