2. Next there is the issue of surface preparation. If the plans say
prepare
by running with 80 grid paper then it is fairly clear that the guy who
wrote
the plans knows little about what he is doing ! Epoxy metal bonding is
reliable if the surfaces are prepared properly but from what you have said
I
doubt that is the case.

I recently did some testing with West Systems and aluminum. I used 3 test
strips, side by side. 1" wide fiberglass tape, 3 inches of bonding surface
on 6061.

The first strip was applied with no surface impression at all.
The second strip was applied after sanding with 80 Grit
The third was sanded and etched with an etch (Duramix 4925)

The first strip came off with maybe a pound of force, pulling on the end of
the fiberglass tape.
The second strip (sanded) took maybe twice that - it still came right off
The third (etched) strip never did come off, I tore the fiberglass tape It
stood up to at least 30 pounds in shear!

Surface preparation makes a BIG difference!.