If you have a Model B timing cover on a Model A it will look fine BUT the timing will always be way off. See below...........
Here's is a great link to Timing Covers.
http://www.fordgarage.com/pages/timingcovers.htm
READ TO THE END. THE FINAL CONSIDERATIONS ARE EXTREMELY INTERESTING AND MAY BE YOUR ENTIRE PROBLEM...IF IN FACT YOU CAN'T SEEM TO TIME THIS. Again I need others here to tell the difference from a Model B distributor and a Model A distributor.