A 305/30/20 is approx. 27.2 inches tall...a 305/35/20 increases that substantially to 28.4 inches tall.if you’re set on 305’s I would recommend getting a larger 11” wheel for optimal fit and performance. Otherwise, the 305’s on 10.5 would work just fine with only the slightest amount of bulge. However, a 35 sidewall would be preferred in that case versus a 30 to minimize that.
I don’t believe you’re in the territory of needing a camber adjustment and that’s with the drop.
https://www.mustang6g.com/forums/threads/whos-lowered-with-305-35-20s.120197/
check out this thread