Not sure what device would be a Model 79.
For coil/condenser/ignition testers, the oldest Merc-O-Tronic I’ve seen is a Model 88.
It was superceded by the Model 98, followed soon after by the Model 98A that had attachment(s) that allowed you to test CDI ignition systems.
I’m sure those were followed by updated versions as well, but that’s as far as my knowledge of Merc-O-Tronic ignition testers extends.
Hope this helps, sorry if it doesn’t
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...