Tires for 14x4.5 wheels?

The alpha-numeric system was based on load ratings. Although you have a goal of not visually bulging, a radial tire will always look a little flatter on the bottom than bias ply construction. It is important the tire is rated to support the weight its supposed to.

Checking my 1975 Plymouth Valiant owners manual, both 6.95-14 and D78-14 are recommended sizes with the 4 1/2 J rims. 5 1/2 JJ rims can use those as well as E70-14, E78-14, ER78-14. So as 2 Darts explained well, probably don't want to use those sizes or their equivalents.

Here's a chart at Tirerack that shows equivalent tires. D78 doesn't have a direct equivalent.
https://www.tirerack.com/tires/tiretech/45_conversionchart.html

It looks to me like P185/75R14 is the closest in terms of load rating without going wider than the rim would want. You can check each specific tire for recommended rim widths. I suspect they'll generally be as 2 Darts has said.