W114 280CE would have been 185 14. The original wheels can fit modern 195 75 14s. I wouldn't go wider as the steering box mounting to the inner wing isn't that strong.
Many owners can benefit from an update to 185[195] /65 x 15 wheels and tyres.This retains almost the same rolling radius [ wheeel tyre combo] and yields a much wider choice of more modern [ and cheaper!]tyres. Car Bibles : The Wheel and Tyre Bible This happened to the model in its later versions anyway so not a radical mod. If you want to retain orginality then of course you should go with Charles Suggestion