69 dart wheel & steering questions

As far as being able to steer that size tire I think it can be done with a manual box. I used to run a bias ply tire about that size (might have been a little smaller, it was an E60 14) on front of my car with no problems. A quick ratio manual steering box might be a different story. I've never driven with one of them. Looking at your pic, you might be able to fit that tire in front okay with the correct backspacing. Mine was 14 x 7 with about 4 3/8" backspacing and a 7/16" swheel spacer.