This "may" help
FORD CODES and SERIAL NUMBERS
The 15011p is the model code. But I am showing nothing for the 1 or the P
The 50 is industrial
And the 11 means diesel and no PTO
The 4A21B is the date code. Made in
4........1974
A........January
21........21st
B.......Dayshift
A256066 is the serial #
Perhaps some pics may help?
Not familiar with all of the ford hoes, but the 4500 has PS in the nose cone and a somewhat swept back from axle. But that model # should have started with a 4 and not a 1.
So are you POSITIVE on those #'s.
Also, is there still an identification tag (little spamped peice of metal) on the loader of BH with a model for the attachments?
And the serial # starting with an A is also puzzling. The letter is usually where they were made. B=England C=USA
Good luck. And the more info and pics, the better we can help