Not precisely. I asked how it should be built, and someone suggested to put a plate on the inside.
It's clear from this thread everything should be aluminum, and consensus appears that it isn't strictly needed. The force applied is greatest at the inside top bolts of the transom and the outside bottom bolts due to the whole thing essentially being a lever. The bolts are stainless only because aluminum bols aren't strong enough (if they even exist).
I personally am uncomfortable using angle for an engine this size, I would feel better if it were at least "c" channel. That is just my gut feel, no actual numbers to back that up. But I have looked at pictures of Z-Lock for comparison. Most notably, the hi jacker design (which resembles the angle design) is rated up to 150hp. For larger engines, the design changes. The amount of force needed to move 2000lbs of boat, plus 1000lbs of fuel, people, and gear has to be significant ... Plus it must apply some amount of torque due to the prop.
[EDIT] Just found this design that uses angle brackets here:
Machine Shop Goes up to 300hp, so maybe angle is OK. I am stopping by a metal place Friday to see what is available and what it costs.