I got lucky; I was given a used TR3 (or 4?) cap, and it's the same diameter as the MGB/Healey filler tubes, only requiring an additional rubber coupling and a pair of OE-type wire-screw clamps.
I'm in the
Dougie Camp, preferring the 45* angle of orientation.
Unfortunately, my web-server is down for some long overdue maintenance, so no highly detailed pictures available (I'd posted this one to FB with my phone, so those are the only ones presently at my disposal
). I hope I'm not offline for too long, but I shipped the server back to Michigan where the guy that built it, wrote the program and built the database is, so I'm at his mercy...