j54,
If you are referring to a Chevy, I am very interested in the answer to this question too. Parts for 48-53 are much easier to come by. They can make a very nice substitute on my 55 first if they fit.
The 1929-1957 Chevrolet Master parts catalog seems to indicate the upper radiator grill baffle part number is 3700834 for 47-55 first. I may not be reading it correctly though because I have pics of two different baffles in my photos (look in the 54 grill album). The baffle I believe to be 47-53 fits O.K. but as you can tell from the pics there are some differences where the grill bolts on.
So in short I think they are different.
Look forward to hearing from tclederman as well. He has a ton of info on the 54s.
