The oil pan does not have to be dropped for a routine oil change. But for many years Packard recommended dropping the oil pan annually to clean it, and that was in the era of non-detergent oil and also assuming a normal amount of driving, perhaps 12,000 miles per year. My own opinion is that before putting any car into service that has an unknown history regarding when the pan was last dropped, then you should do it before returning the car to service and with typical collector car useage and modern detergent oils, perhaps once every 7-10 or so thereafter.
If the engine is frozen, dropping the oil pan with the engine in the car can be difficult on your 47 as the forward shallow part of the pan sits very close to the crossmember and you will almost always have to rotate the crankshaft once or more to move the counterweights up out of the way in order to slide the pan rearwards. If that is the case it may be necessary to remove the front motor mount and hoist or jack the engine up a few inches.
You might get some further ideas on returning this car to service from this (not necessarily all-inclusive) article:
http://www.packardclub.org/forum/viewtopic.php?f=14&t=859This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=113201