1974 Dart Wheel Size ?

As for measuring the bolt pattern it's probably the the 5x4.5 my 73 has the BBP

but try this

http://www.mrt-wheels.com/boltpattern.html

The conversion stuff is pretty easy to come by (if you have the dough). discs and calipers are still available new from pepboys. spindles - junk yard
might even be able to reuse the upper control arms if it's a 74