Wheel questions/68 Barracuda Coupe

At this point, I want to print all these threads for a how to book. I know a lot less than I thought and you guys have really helped me. Great advice. I want a fast ride but I'm not a racer or hot rodder either. I would love to drive my car to work every day. I'm not sure the brake drum size yet. Guess I can figure that out tomorrow. How do I measure? I didn measure the rear wheel the way you all explained it and yep, 4" bolt pattern. Would it be a real mistake to stay with drums? I suspect mine are 9 inch. I was looking at the Strange Dana60 axle set up and they are 11" if I'm not mistaken. Again. you have given me valuable advice.