Earl seems to have had a preference for rounded, as opposed to more angular, sculpting. Those designs introduced in '54 and '55 were less rounded than before. So for the 1957 model year redesign of GM's more upscale B- and C-bodies, Earl moved back to his preferred rounded surfaces.
Unfortunately for Earl, Chrysler Corporation redesigned its entire line for 1957 in a manner that made his new designs seem out of date. Chrysler Corporation cars features low hoods, thin rooflines and bold tail fins. That is, much less rounding than GM was doing.
Earl was nearing mandatory retirement age, and many on his styling staff began crash-project studies of angular designs for the 1959 model year while Earl was in Europe for his annual studies of new car designs there.
That's the story I've found in many places. A story about the massive 1958 facelift of '57 Oldsmobiles and Buicks is lacking, at least in my reference library and results of some Googling on the internet.
Designs of 1958 GM cars were largely in place in the fall of 1956 when some GM stylists viewed forthcoming 1957 Chrysler cars in a storage lot. Photos of 1958 styling models for Buick indicate that sheet metal changes were already planned, given normal tooling lead-times, before 1957 Chrysler styling was known to GM. Trim detail alternatives seem to have been under consideration as late as early 1957, according to the book "Designing America's Cars: The 50s" -- Amazon reference here. I think that might be a little later than what happened, given tooling and publicity needs. Unless the '58 Olds and Buick facelifts were also crash projects.
Harlow Curtice was GM's Chief Operating Officer from 2 February 1953 to 31 August 1958. In the 1930s and'40s he was President of GM's Buick Division, and tended to favor it later as he continued his upward path in GM's executive hierarchy. In those days, General Motors was financially rich, dominating the American automobile market. It could afford major facelifts and crash projects. Chevrolets and Pontiac were given major facelifts the final year of their 1955-1957 run. Buick was given notable facelifts over its B- and C-body 1954-1956 run -- front end designs being changed both for 1955 and 1956. I suspect Curtice was happy to approve tooling funding.
So there clearly was precedent for major facelifting of 1957 models for 1958. And 1958 GM designs were not a reaction to the 1957 Chrysler line. Nor could they have been, given development time requirements. Those overly decorated 1958 Buicks and Oldsmobiles were largely a matter of Harley Earl in desperation for viable new styling ideas.
Unless noted, images below are of cars listed for sale.
Two-Door Hardtops
First, B-body two-door hardtops. The hood is flat, while the passenger compartment greenhouse roof is high and rounded. Buick's traditional Sweepspear side trim serves define two-tone paint areas.
Not shown is the revised front end. The backlight window is larger. Slight smoothing at the front of the rear fender. Rear wheel opening reshaped to allow that large chromed shape on the rear fender. It visually conflicts with, and encroaches on, the Sweepspear. Surprisingly unprofessional detail styling from GM.
This rear quarter view shows the unfortunate backlight window design that was not popular with potential 1957 model buyers. The problem is the rounded framing of the outer windows next to the central segment. Sharp framing next to the sculpted flow-through from the roof to the trunk (not necessarily a bad thing, that sculpting theme) would have largely solved the defect.
That framing was abandoned for 1958. Tail light framing was reshaped and chrome added to the top of the rear fenders.
Now for C-body 2-door hardtops. Again, low hood and rounded greenhouse. These cars had longer wheelbases. C-pillar slants back, conforming with the backlight window,
Side trim changes the same as on B-bodies. The fenderline now drops below the beltline, requiring new stamping. The C-pillar is now chromed.
Similar to B-body versions. Some line-topping Roadmasters had narrow chrome strips running from the roof to along the trunk lid, dividing the backlight into three segments. That was aesthetically okay, being much less ponderous than the window division scheme on B-bodies, as shown above. Front fenderline is slightly dropped.
Similar '57-'58 changes here.
Four-Door Hardtops
B-bodies. The greenhouse window profile is similar to the of the 2-door hardtop, but adjusted for the presence of the added doors.
Unlike the 2-door hardtops, the fenderline is dropped below the beltline.
Again, the unfortunate backlight framing.
Same changes at the rear.
Now 4-door C-body hardtops. This monochrome car seems attractive in side-view. Aside from the heavily chromed aft trim.
The wide C-pillar is replaced by a small side window. Front fenderline is a bit lower, making the hood appear, or perhaps slightly be, higher (something Earl liked).
Those trunk lid chrome strips in some cased extended up across the backlight window and then over the roof, as noted above.
Buick's new top-of-the-line model for 1958, the Limited, lacked the chrome swath on the rear fender. Its outline trim piece was retained. On the painted area inside it perimeter were three sets of slender chrome slashes set at the same angle as the fender aft and. This was more tasteful, but the frame continued to clash with the Sweepspear.
