Old ford part numbers
up until the late 90's the key was:
first letter of prefix = decade
b=50, c=60, d= 70, f= 80, e = 90
Second letter of prefix = year
so D5 = 1975 -- this is the first year that part was in production -- however the part may stay in production for years
So that just tells you it must be at least that late.
further third letter is related to application designed for:
A= Ford D= fairlane or midsize T= truck Z= mustang
but you can't go by that because if the part is the same across applications, it uses the letter it was first released under.
Fourth letter is design responsibility E= engine engineering, P =automatic transmission engineering, B= body engineering.
Middle is base part number, doesn't change across cars. 6015 is an engine block, no matter what family.
Suffix (often AA) is used to track engineering changes across minor revisions.
So you know the engine was built after 1975. Manifolds usually change with major vehicle packaging, so it is probably within 4 or 5 years of that, but that's not a sure thing....
If you can see numbers, check the block. heads and intake
Those are the parts that would matter most for any kind of practical purposes