How do I tell what tranny this is?

If it's the factory transmission, it'd be a T45. Not possible to swap into a 5.0 powered Mustang because the bellhousing bolt pattern is different than a 5.0. It may be possible that someone makes a bellhousing to use a T5 with the 4.6, but I don't know why anyone would go to the trouble of swapping one weak trans for another?

are you sure that this number is correct FGZR 7003 CRES AA M2053
1381 001 20715E.....look again in the first four digits the second digit should be a number see if the first four digits dont read F6ZR which would mean its a 96 model tranny which would be a t-45...plus the t-45 bellhousing bolts on from the inside and the t-5 bellhousing (not shown in pic.) bolts from the outside the bellhousing by four bolts thru the gear housing which can be seen on all four corners.and also notice the differences in the drain and fill plugs...

t-5

View attachment 402474


t-45

View attachment 402477