I too have the commando bumpers. I've wanted to alter or replace them, but lazyness prevails. My front bumper should have been a black one but a previous accident repair left it with a silver one. At the junk yard I grabed a spoiler. Turned out to be a later style. This opened up all sorts of mounting options. I chose to remove all the bumps and other high spots so it would be mate evenly with the bottom of the bumper. I also cut it in the middle and added a section to the spoiler to widen it. That way the spoiler goes all the way to the edge of the bumper. It wont win any concours medals, but once its paited black it gets the job done.

If the spoiler came from an 84, it should fit an 83 or a 90. In fact, the spoiler from an 84 is the same as the one that came on all the late models. It sounds like it probably came from an earlier car with the commando bumper, in which case it won't fit the later cars.
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1991 245, 61k miles, looking for a 5 speed 92-93 245 cheap.