Not sure about the N/A 3800's. I know the S/C throttle body is different than N/A throttle body. I've seen quite a few L67's in the last couple of months while scrounging the yards. I just never see them in Grand Prix's. Because we live in old folks country, I've always seen them all in Regal GS's and Buick Ultra's.

I would still try returning what you have. Be honest and explain what happened. Probably just give you a credit. Better than nothing.