Find the engine code on the flat boss just to the rear of the distributor.
This site gives a nice explanation of how to interpret the code.
http://www.novaresource.org/codes.htm
This site gives more info on that generation of sixes and expands the listings of the engine code suffixes.
http://no25.chuckthetruck.com/index.html
Hope this helps.


"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson