Not sure about the seats from the Cobra, but I think you could probably make them work if they don't bolt directly in. If you decide not to go with those, check this out:
http://www.saunders2000.com/HBS/group.htm
It's a group purchase on Corbeau seats. There are several racing seats listed that you might like. Savings are about $30-$50 off per seat.
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1991 LX 5.0 Convertible
AOD w/ shift kit
Chassis:
Steeda cross-brace SFCs, Steeda G-load brace, Steeda strut-tower brace, 4-pt. Autopower roll-bar
Go-fast stuff: FMS 3.73s, K&N minus air silencer, MAC unequal length shorties and cat-backs, bad-ass Firehawk SZ50EP tires (225/55 16)