Most mid century FoMoCo models were 6 X 9 types but many had a powered coil since there wasn't much room left in the dash for a big magnet. There are some replacements being manufactured with very low profile magnets that will work.
http://www.turnswitch.com/speakers.htm
What type of 49 is it? I bought a 6x9 from the junkyard out of a newer impala and it bolted right into my F1.