Here you can see that I installed jumpers to make half of the fuse block to be constant-on 12V and the other half to be switched. As these are the feeders, I used heavy gauge wire. The switched wire is the short one below, it goes over to the first fuse block and picks up the switched circuit. The unswitched wire goes all the way back to the 12V auxiliary battery terminal for the cleanest power source.
Richard Rodriguez warned me about poor grounding that he found during his conversion, so I cut the big, fraying, single-gang grounding bundle of brown wires into several smaller ones, crimped on connectors and heat-shrink tubing and secured them down on the grounding bolt.
I drilled and bolted the second fuse block into the first one, and it was a very tight fit!
The one thing I didn't count on was the position of the battery circuit breaker. The downside is I lose a couple of the unswitched fuses. The upside is the back of the breaker's housing holds the second fuse block securely in place. This will all look better when I install the carpet and tidy up the wiring.