The label VAI has been acquiring and issuing many of those live broadcasts of musicals from the 1950s -- including that Connecticut Yankee! Which did indeed have Boris Karloff, along with Eddie Albert and Janet Blair. Others on their list that I've acquired include

Bloomer Girl with Barbara Cook
Kiss Me Kate with the two original stars
The Mikado with Groucho Marx
The Yeomen of the Guard with Barbara Cook, Celeste Holm, and Alfred Drake

and they keep bring out more every month. Good to know about.