I'm not sure where you got the tag from but we normally go by casting numbers.
Block casting numbers are just under the starter motor on the passenger's side. They should look like common Ford numbers (Ex: D2AE).
The first digit, 'D' is the decade. 'D' is in the 70's.
The second digit, '2' is the year. So, 'D2' is 1972.
The third digit designates which car line it was made for:
Casting letter, 'A' - full size Ford, (C) Torino/Elite, (J) Industrial engine, (M) Mercury, (S) Thunderbird, (T) Truck, (U) Econoline van, (V) Lincoln.
There are base numbers that designate what part it is, like D2AE-6015-A. We already know the prefix but the 6015 means it is a block.
6090/6049 casting numbers are on cylinder heads, 6110 are on pistons, 6205 denotes a connecting rod, 6303/6300 a crankshaft and 9425 denotes an intake manifold.
I would be guessing at your numbers because I don't know where this tag was located;
460 68 2 <--460, built in 1968
8-J Ford K875 - S <--http://fordification.net/tech/engineIDtags_cars.htm
'S' could mean it was in a Thunderbird.