'68 Sagging spridget

Buddy of mine has a '68 Midget that sags on the passenger side such that the
door doesn't close without use of extreme prejudice.  No visible reason for
this...no great rotso.

I am assuming that the cause of this was the POs poor "restoration" of this
car, but anyone have any suggestions as to a fix?   We have access to a
concrete floor with pulling pots in it....should we attempt this ourselves?

GJB