This is the best that I have, it shows one of the mounting points on my SPF 289 FIA when I had the interior gutted. You can see the inner most leg where it attaches to the frame near the tunnel.
If you are looking at an FIA, there will be a similar brace point forward on the passenger side frame rail approximately underneath the front hoop/dashboard. On a 427 style there will be a rear brace attached to the frame behind the driver's seat. From what I recall from my 427 ERA, there was a raised bracket coming up from the frame for the rear leg, it does not go all the way down to the frame as the diff and hubs are in the way.
Jim