For the 54-55 Manhattans, the supercharger was standard equipment. Early and Late only applies to the Specials (no supercharger). The Early Specials were left-over 53 cars, and had the one piece rear window, 53 interiors, and had the front and rear ends grafted on by putting in new trim holes etc. The Late Specials had the three piece rear window etc, and were the 'real' 54 cars. Some Manhattans have been robbed of the supercharger over the years; conversely, some Specials might had had it added, and the 'script' updated.
As soon as you have the info/car deal sealed and can tell us all about it, look at the Registry and see if this car is already there. If not, please send an email there and update it with all the serial# and cowl plate information. Then come back and tell us all about your new baby!
cheers, Jim Bartley