Well, what I've found available:
CF Tube; OD: 5.30", ID: 5.00", Wall Thickness: 0.156"
CF Plate; 0.197" Plate Thickness (to be cut to 5.30"ma elliptical shape)

So, for a 6"ma Pyrex secondary, 1.5" thick, three dots of silicone ~0.6 to 0.7" diameter, placed at ~72% of radius, which equates to 4.32" circle, with the lowest dot at 6 o'clock and the other two dots above at 120 degrees with a target thickness of ~0.055" per dot.

Will that plate, at 0.197", be thick enough? The three pads will be nearly to its edge where the tube provides support so I think so. I'll also be putting a central hole pattern in th plate to pass air through the enclosed tube structure and past the secondary backside for cooling.

And, four non-contact mirror clips bolted to the tube and wrapping around the front surface, for peace of mind.

The CF tube at the other end will have a 5"OD 1/2"T aluminum plate plug for the collimation screws to push-pull against for alignment, with the second plate having the threaded rod to attach to the spider.

Any thing here look to be a problem? Elliptically cut tube with elliptical plate and aluminum plug at each end, that construction is a little different than an RC scope holder.... Any suggestions?

Steven