It's the 5th digit of the VIN. It tells which engine was factory in that car. T is 200ci I6, C is 2bb1 289, A is 4bb1 289, K is 289 HiPo, F is 2bbl 302, J is 4bbl 302, Q & R are Ramair & non-RA 428CJ/SCJ, S is 390, X is 390 2bbl (68 only). There are more, but this is all off the top of my head.
The squirrels in my head have spoken.
Cobra 5.0L & AOD swap, here we come.