I am not sure but I donít think PEX was around in 1978. I have an 87 and it has polybutylene, or something like that. The Sharkbite may still work but I believe there are different versions of the Sharkbite fittings. Measure it closely and go to a plumbing store and ask them. Some are metric size also.
If you are one there is no explanation necessary.
If you arenít one, there is no explanation possible.