First off, let us drop the utterly misguided moniker 'redtop' from the discussion; save that for the kiddiwinks with their zorsts & cones. In any proper engine discussion the use of that description only serves to confuse.
I didn't realise that there weren't any LETs after 1996.

And what made you erroneously start thinking there were?
Tis quite easy really. First came the 20XE. NO cat, 156ps
For impending Euro1, this was tweaked by having a CAT + Motronic 2.5, a closed loop ( lambda running) ecu, fitted. This engine is the C20XE, 150ps. The Turbo version, C20LET,204ps, followed in 1992.
GM , like most others, changed over to Cat engines well before the deadline for Euro1. AFAIK, the Calibra was never fitted with the 20XE; however legally you can remove the Cat on pre-Aug 1992 cars.
Euro2 had to be implemented by the end of 1996. GM replaced the brilliant C20XE with the pathetic X20XEV,136ps to meet that emission standard. Naturally the C20LET was dropped, it's eventual replacement being the Z20LET( with variations) which was never fitted in the Calibra.
For those still unable to grasp the extremely basic camcover 'L' plate identity scenario, there is a similar thread running concurrently here
http://www.clubcalibra.com/index.php?topic=26072.0