The firebird has a much lower roof ht.I am 6'3" and find it hard to get comfortable in my 72 camaro.even w/the seat as low as it will go and still slide back and forth.My head still hits the under side of the roof.So if your a tall fella,I would look into the caprice.The firebird is more suited for somebody that might be shorter.
I like both choices but if I'm looking down the road and ROI (return on investment) is a factor, the Firebird gets my choice. I don't see much of a market for the Impala/Caprice like I do for the Firebird.
Firebird without a question would be my first choice.Caprice would probably need much more fab work and one off custom parts to make it look and perform as a true badass PT car.
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Stefan B. Do what's right,not what's easy!