I just pulled the engine out of my 90 Mustang. The block has E7TE stamped in it, Date cod LF111618. The heads are E5TE. Do you think there was an engine swap at one time?
Doesnt sound like a motor swap to me, or if it was it was the same motor that was taken out. E5s were offered around the same time as the E7s (which generally speaking are crappy heads too). Thinking they have bigger Combustion chambers (69cc), lowering your compression a little and a massive thermactor bump in the exhaust. They seem to be pretty similar heads but definitely arent the same.
Date code should only be 3 or 4 digits i believe.
Example: 9B7
9= year (C, for example, was 60s so it would be 1969)
B- feb and
7 - the day.
so It was made on Feb 7, 1969.
If you have pics, im sure someone could tell you what you need to know