I may be wrong, but I think they are the same, except the models with the power rear seat. I think the extra length was in the rear footwell area. Please correct me if I'm wrong, but I thouth the SEL was about 4-6" longer, mainly in the rear footwell area, with a longer rear door.

My question would have to do with the power/heat available on the later models, and how hard those features would be to integrate, relays, wiring, switches etc. (front seat, doubt reclining rear seat would ever work)
-Zach

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1978 240D Auomatic
Custom Charcoal Gray, Navy MB tex, kenwood/Elemental/Boston/Aura sound,
Shaved antenna and emblems.

1990 Lincoln Town Car, Sleeper/Strip car in progress, 17.75@77mph.