One thing I learned about fiberglass deck lids is that they cannot use the stock lift cylinders. You have to carry around a stick to prop it up. This may not be true for all lids, but something you may want to check out before you buy one. Other than that, I might just hit a boneyard and see if you can find a decent used one there.
Good luck, and let us know what you end up doing.
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See my
1985 Mustang GT