I believe the top number is the year, motor size, month and day...Someone else could verify this and chime in with the rest. Good luck interesting question.
Normally the P273 would reference the model year IE A273=1965 B273=1966 C273=1967 and the other number 4-27 the date the engine was assembled.
Now unless the P is actually a B I cannot comment. As for the 2250? no idea.