As can be seen below, the differences were not made by modifying some of the bodywork as was done for 1953, but instead done by simply attaching panels on the rear fenders. No doubt there were some interior differences as well, but our focus in on exterior appearance.
1953 Cadillac 62 Convertible - Mecum Auctions photo
Reviewing 1953, here is the basis car for the Eldorado modifications.
1953 Cadillac Eldorado - Broad Arrow Auctions photo
The major differences are (1) a flowing beltline by the passenger compartment, and (2) a panoramic/wraparound windshield. 1953 Eldorado and Oldsmobile Fiesta convertibles were given panoramic windshields with the idea that these would help condition potential 1954 model year buyers that wraparounds were a desirable wave of the future. Furthermore, those convertibles were priced much higher than ordinary convertibles -- Eldorado vs. Model 62: $7,750 vs $4,144; Fiesta vs Model 98: $4,453 vs. $3,229. These higher prices were in part a statement of relative prestige over "ordinary" convertibles and likely also to help defray the added tooling expenses for such low-production cars: 532 Eldorados, 458 Fiestas, and 1,690 Buick Skylarks that featured the flowing beltline, but lacked the wraparound windshield.
1954 Cadillac 62 Convertible- car-for-sale photos
The basic Cadillac convertible for '54.
1954 Cadillac Eldorado Convertible - BaT Auctions photos
The Eldorado. It was priced $5,738 vs. $4,144 for the Model 62 -- a much lesser ratio than that of the 1953 cars. Eldorado production was 2,150 -- nearly four times more than for '53.
All 1954 Cadillacs had panoramic windshields.
The main exterior difference is that aluminum panel on the rear fender.
Internet images suggest that most or all 62 convertible tops had canvas covers when retracted.
Whereas Eldorado tops were housed under a solid cover.