Hi,
As far as I know, there are three places that give you numbers.
1) on front, often says something like 66 352 and you get the 352 number on just about any FE
2) on Back it will give the a block number EG 390 but this doesn't mean its a 390!
3) on side near the bottom something like C6AE-F (I made that code up)
This will help decoding it:
http://www.classicmustang.com/decoding_part_numbers.htm
If you lucky there is a metal tag under the dizzy I think (not on mine though
) with more detailed info
Hope that helps, I'm not too sure there is any number that definately identifies an FE as a specific engine (428CJ, 427SO etc)
except maybe the metal tag if you have it.
Good luck
Paul