Russell Duffy wrote:

I'm now wondering if I couldn't just put about a dozen 1/8" pop rivets, rather than welding the angle.  I have to admit, that I'm thinking about easy of replacement if one ever gets damaged away from home.  Assuming I keep a spare core with two AN12 fittings welded to it, all I'd have to do to replace a core is drill out the rivets, then drill and pop rivet the new core.

That's the way I did it (but also JB-Weld inbetween the angles and the cores - probably not needed). Well, actually I do have two 1/4 threaded rods on the outside of the cores connecting the upper and lower angles.
However, both Tracy and Ed have rubber spacing  - basically clamping the cores between their mounts.
Tracy's comment was that my installation would never make it in a Lycoming environment (vibrations).
I never fully understood that - if cores are solidly mounted to the engine there should be no realtive motion...

Finn