Best tire pressure for 69 dart with P245 60R14

Can't see the brand and style but 99.9% odds those are aluminum alloy - not magnesium alloy.
Magnesium quickly turns gray if not maintained and is big $$$.
Most important will be the correct bolt patter for your car, and back spacing that will work.
Check on the type of wheel nut it needs. I've been lucky in that all my used rims came with correct matching nuts - even the lefthand threads.

This is website has decent overview of the many of the early 'mags' both aluminum and magnesium. It will give you an idea of what was made in each.
Classic racing wheels

Crager SS and many others early classics were aluminum center with steel rims.

This company seperates the wheels (used) they sell by material.
AKH Vintage Wheels - Vintage Rally, Styled Steel, and Alloy Wheels