Handbags (The sad, the bad and the ugly. Non-productive stuff here.)
A signed permit from 1973 will not suffice. You've carried out non-permitted work. If anything fails causing damage you'll have no recourse with the insurance company.
You may not be worried now, but you will be when your staring at a pile of ashes.
Hope the wiring and receptacle were UL listed.
Replied: 16th May 2017 at 22:09