Well, true confessions...
While attempting to hang my upper cabinets to the wood anchor blocks I had cemented to the shell (as described earlier) the glue failed and the blocks broke free!
I do not know if this was user-error or if I was expecting too much performance from the cement, in any case, I had to find another way to attach the blocks to the shell with complete confidence that they would not fall
(BTW, this was not an issue for the blocks used to keep the LOWER cabinetry tight and in place. Gravity and floor attachment points did not allow as much stress on the wall blocks as the UPPERs were creating.)
My solution? Three stainless steel carriage bolts. It' a bit complicated, but here's what I did to insure a strong and leak-proof connection:
1) Through the shell I drilled a hole to the exact width of the bolt shank.
2) To this hole I took a small flat file and made the round hole "square" in order to receive the square neck of the carriage bolt. This step insures that carriage bolt could seat into the shell and NOT spin.
3) I then wrapped the top end of the bolt's threads and neck with a bead of butyl putty, pushed the bolt through the square hole until it "seated" tightly against the FG. Inside I added a small SS washer and nut, then tightened until the butyl putty eased out. The tight fit and putty should prevent any water infiltration.
4) To my new plywood block I bored a hole for the bolt shank AND a shallow void to allow the nut/washer at the shell to "countersink" into the block.
5) With a liberal amount of construction adhesive applied onto the block and filling the countersink hole, the block got pushed onto the shaft and squeezed to the shell. (This glue will also help prevent water leaks
around the bolt, should the butyl putty fail.)
6) Another SS washer and nut then got spun onto the bolt shaft and the block was tightened to the shell. BUT not TOO tight, just enough to squeeze out a little adhesive. Overtightening could either distort or crack the shell exterior.
7) With the adhesive dry, and the bolt insuring that there was no way for the block to pull away, the block was now firmly affixed to the shell, and ready to use as an anchor for my cabinets.