The single best thing you can do is add a relay. Right now all the headlight power goes through he switch. By adding a relay the headlights are powered by the relay and the dash lights by the headlight switch. It takes a tremendous amount of work (amperage) off of the old wiring. The dash...
One of my Mustangs was stolen years ago. It didn't have an ignition in it. I was upgrading to a Crane. They pushed it! They want it they are going to get it
I would just make sure the heads are gone through by your machinist.
Tony here are the CHI heads
https://7173mustangs.com/threads/1973-machi-restoration-for-my-wife-for-our-20th-anniversary.28508/page-3#post-385607
I went with original Boss valve covers but I think everything else is aftermarket! The March pulley system did not fit. It was close but required machining. My wife likes it shiny so I left the bling. It's almost ready to run
Unfortunately, that needs to be stretched there is really no way to do this without access to the back. If you use a dent puller you will end up with a huge mess. It needs to be replaced or filled.