Road Runner Nest

Does anyone have the mounting location for the chin spoilers on a 71 road runner?

They were dealer installed, so there's no factory correct location. Here's a couple previous threads.
http://www.roadrunnernest.com/forum/vie ... hilit=chin
http://www.roadrunnernest.com/forum/vie ... in+spoiler

I don't have chin spoilers on my car, but there are a series of holes across the bottom of each fender. I assumed that they were for installing them if necessary.

I've been thinking about adding a pair of chin spoilers to my 74 RR, but I keep hearing from the sellers that they won't fit because the front valances are different for 73/74 compared to 71/72. Has anybody tried a set on a 73/74? I'm curious as to how much rework I need to go through to make them fit, BEFORE I lay out the $$.