WOW! I looked at the pix, and if it were me I'd get a new frame. If it was under a hardtop I'd say weld away. Converts require a boxed, strong frame or they would fold in half. If you were to acid dip it, I think you would have next to nothing left. Station wagons and El Caminos used the same type of boxed frame. I'm not sure if they would be a bolt in without mods, but it would be worth checking out. My $0.02!
PAWN SHOP FIND
RESTORATION IN 1980...
"You can have it all, my emipre of dirt. I will let you down, I will make you hurt"