According to Ford lit. for 1970 I've seen, 14x7 wheels were used on 351C-4V and 428CJ/SCJ cars. 14X6 wheels were used on the rest. I've read posts from those with 351-2V cars saying they had 14x7 wheels, and maybe that's how they were delivered, but the Ford dealer info shows it the way I've stated. I've never seen anything that suggested any difference for the type of brakes - there would just be no mechanical reason for doing so.
I can't comment about the base trim ring/poverty cap wheelcovers, but the sport wheelcovers came in two sizes (two part #s); one for 14x7, one for 14x6 wheels. The only difference between the two is the depth of the integral trim ring. For this reason, I'd worry the trim rings in your case wouldn't interchange between the two size wheels. The Ford parts book (sorry, mine isn't handy right now) should show whether two different rings were used and perhaps dimensions along with the part numbers.
