Gus,
My concern was actually a bit more subtle than it might have appeared. Your suggestion to build it and measure the resistance is a good one - the obvious solution.
As a 30 year plus electrical engineer who has worked in the aircraft design, flight test, and mod industries over a good portion of that time (although that was several years ago), I take AC43.13 to be gospel. My concern wasn't the primary grounding to the structure (as shown in the 43.13 diagram that Walt posted), rather the creation of non-bonded ground paths and ground loops caused by having more than two layers of metal with primed feying surfaces riveted together (consider a wing spar with double spar caps. In that situation, priming of the feying surfaces isolates the web in the middle. The rivets through the assembly only make contact on the outsides of the assembly via the undersides of the heads, leaving the bonding to the web to be kind of doubtful as it relies only on incidental contact with the rivet shaft. This is kind of similar to what happens when 2 fully primed parts are riveted together. Will that be enough to guarantee bonding? I suspect that it will, but we will see.
I will do a short experiment and post the results, if anyone is interested.
Doug