Passenger Side - The easiest way to distinguish a 1948 model from other years is to look at the instrument panel. This year of Cadillac had a unique "horseshoe" design matching the curve of the steering wheel. Note the original dash, stock door panels and sliding glass partition window.
Note that a modern (1967 Cadillac?) tilt steering wheel was added; locating a stock 1948 steering column replacement is relatively easy since entire 1940's Cadillac steering columns frequently are offered for sale on eBay for under $90 (e.g. eBay auction 280279061818 ending 11/1/08).
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