I'm not sure what if anything is different between an '81 and an '85 (mine) but here's "how to" for an '85 Cab: To remove the side grill on a Mondial, find and remove one phillips head screw up inside the top rear corner of the grill. CAREFULLY, push the entire grill towards the front of the car to release the plastic hooks under the front ends of the fins (The hooks are facing towards the rear of the car and are catching on slots in the bodywork sheetmetal underneath). Do not pull the grill away from the car body until the "hooks" are released from their slots at the ends of the fins! CAREFULLY pull the ends of the fins away from the body, working each one out a little at a time (not all at once). Mine was gunked with years of wax buildup and took some coaxing. Don't break the hooks - they are a molded part of the grill assembly and are fragile plastic. Hope this helps. Just be real careful.
same deal on the `81. although mine are cast aluminum and VERY fragile. once off be carefull where you rest them. the rest of the assymebly comes out from inside the engine bay and requires removal of the oil cooler on the driver side and the A/C and coolant hose on the passenger side. i take mine off once a month to wax and clean.
On the "t" they are also cast aluminum and they are kinda unfinished on the inside and the removal process always poses a very serious "scratch" threat to the modial paintwork in the are of the vents.