I've been thinking... there is another het pairing I like, and you might even know of that one too, since you're familiar with 1970s British TV. :) I'm planning to start a re-watch of Upstairs, Downstairs next weekend, and I think I've been mentally shipping Richard Bellamy/Hazel Forrest since I saw it for the first time. I've requested this pairing a few times in fic exchanges too; never had any luck, but there's at least one fic on AO3.
Now that I think about it, the dynamic bears similarities to Mina/Van Helsing. Hmm. lol