Well...the rib will definitely make it look like a popular 'glass body... Can't recall their name, but they were all ribbed.
Used a 67-72 Chevy Suburban on a Model A Vicky, fit fantastic after moving it around a little. Can't remember if I used the front or back portion, the remainder got used on a 28 Essex coupe
I used an '86 Toyota minivan roof. No ribs. Here's the picture-heavy thread: http://www.jalopyjournal.com/forum/threads/28-tudor-update-6-steel-roof-covered-by-stock-vinyl.636247/ But the better response to your question is to recommend that you make a plywood template of your roof's crown, and take that with you to a junkyard. That way you can find something local that will fit, instead of hunting for specific recommendations that may not exist anywhere near you.
I have used 70's Chevy van (full size) and 70's Chevy Suburban on a few model A sedans, both ribbed with the Suburban having a wider spacing on the ribs (couple inches)
I used a Ford Fairmont roof when I did the last Model A pickup, the one before was a Volvo roof. I also used a 55Chevy wagon roof turned around backwards on a 34 Ford sedan. I like smooth no ribs.