I'm afraid I'll have to agree......these things look semi-ok, but not quite ok enough imo.
IF they couldn't be made in Halogen any better than they were then why not just good old standard incandescent seald beams as the originals were and WITH the right logo whatever it was/is.
I believe that an early Mustang's headlight wireing system CAN tolerate the Halogens provided that is is in good shape with a QUALITY headlight switch to back it all up, I've put Halogens in my old '78 F150 and never had any trouble, and again back in the day my FIRST '65 Mustang had light switch issues way before halogens were invented.