Would you put 13" slicks on 10" rims?

Okay, I took a plumb bob and measured the width of the tubs and the distance from the inside of the tub to the front of the brake drum. The tub is 18 1/2" wide to the top inside of the fender lip, and the brake drum front is 9 1/2" from the inside of the tub, so 9 1/2" space to the inside and 9" to the outside of the brake drum face. If I go with a 12" wide rim with a 6 1/2" backspace and a 12" wide tire with a 14" section width, that should eliminate the contact surface and sidewall issues. Adding for section with, 6 1/2 + 1 for section width = 7 1/2" for the inside which leaves 2" of clearance. 5 1/2 + 1 = 6 1/2" for the outside which leaves 2 1/2" for clearance.
Any red flags before I press the BUY button??