Not true!! 8 1/4" have a cover! If it is the original small bolt pattern it is a 7 1/4", if it has the larger 4.5" bolt pattern it is either a 7 1/4" from 73 and up or an 8 1/4" from 73 and up! Either way it would have to have been swapped in there at some time!
Measure the bolt pattern and report back! My guess is that it is the original 7 1/4"! Geof