Well the 603 should have almost as good reliability, a little more power, and better fuel economy. However, that isn't worth a $1500 premium to me. And the seller thinks it's a V6. If you can talk "V6" way down on price, it would be worth it. Otherwise I'd go with the '84.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.