Teknetics Mark 1 will accept both types of connector (Push-turn & Push only) type.
And I agree, The Mark 1 and Mark III with push type connector it's short. Connector may disconnect out in the field if bumped, but it will work.
Another problem, If memory serves me right I believe Fisher added a dummy pin on some later coils. Instead of push-in 5-pin, it's a push-in 6-pin but one pin is a dummy. As long as the connector is push type, Removing the dummy pin then the coil work's with both older Bounty Hunter series and Older Teknetics models. Then, I heard they went to a threaded connector so that will require changing connector.
Sven posted below a Link to different types of coils for the Mark 1, with a special connector the older White's coils from same era of Teknetics the coils will work. One coil not pictured with the others was the 6" Shooter coil, it works well. Lost my last special connector, so recently replaced plug with a Teknetics Push-turn type on the 6" Shooter coil. Coil operates great with the Mark 1, but I recommend staying with the stock 7.5" Teknetics coil that coil is great for both small targets and gets decent depth. Plus, Lightning separation.
Don't go smaller than 7.5", unless you have a 6" Shooter coil. The 7.5" stock Coil is tough to beat, it's auctally better than the 6" Shooter coil. Anything smaller you're loosing depth, separation isn't really better with anything smaller in fact terrible. Especially the older Bounty hunter 4" concentric coil, it's a dog with the Teknetics Mark I or Mark III.
Good luck, and thanks for sharing the gold coin information.
Paul