Those heads are not CJ heads. They are std small valve FE heads. I'd also check the bore and stroke before any money changes hands to be sure it's at least a std 428. It's possible it could be a 360-390.
Yep you need to cut part of the shock towers and weld in the reinforcement plates. I think Crites has a kit. Or remove them completely and install the proper support bracing. The Twang II suspension is the right way to go
Here's a site that might help you ID things a bit further. Mustang 428 Cobra Jet Registry
click on the component ID section and browse around the block, heads, intake, crank, rods etc...sections.