If you pull the boot around the shifter it will have 6 bolts holding the shifter down. 4 rear ones will be square and the two in the frontfront will be offset towards the center. A t5 will only have 4 bolts holding down the shifter and a tko500/600 all 6 bolts will be even with no offset.
Kevin
The 3550 is the same outside as the TKO showmn in the photo.
Tremec 3550's are almost bulletproof. Use the right lubricant (GM Syncromesh black) and avoid shifting without the clutch and they will outlast the rest of the car.