Here's a great illustrated listing of RCA 2-track (and half-track) monaural and stereophonic tapes.

Thanks, Mikkel. I've seen the Sonotape listing but not the EMI. I presume John has all the tapes he's listed. Impressive. Have you met him?

I recently sold him one Westminster tape he didn't have. (I made a digital copy of it before I sold it.)

I checked the EMI listing and it looks like he's missing many of those tapes. When I was in London in 1965 the HMV music shop was still selling many of the half-track mono titles, along with a few of the 'Steresonic' titles. They were expensive, but I did buy one. And John's listing doesn't include those sold in the US under the Angel label.