The 70 Mustang here as the same leaf width and has way more inner tire clearance, like 1", than the Falcon when using the same exact tire and wheel. Has to do with the seat location on the axle and under car locating points. As for 9 vs 10, the 10s are more common and maybe a couple of $ cheaper. But if you need more contact patch, taller gives more contact than wider. Going from a 26x9 to a 28x9 would increase the contact patch more than going from say a 26x9 to a 26x10.