I've also purchased some products from Spirit. Spirit does not have an assembly manual, but they do offer a CD that has a couple hundred photos of one of their kits being assembled. Their photos do show the proportioning valve installed in the front line. I've always thought that a bit strange, UNLESS you were using the very narrow 'bicycle' type front wheels and tires. This is not the case in Lance's project. I agree that the proportioning valve should be on the rear line. When I plumbed my chassis, I considered putting a proportioning valve on both the front and rear so I could have the option later on of using the narrow tires up front or switch later to something a little more beefy up front (one or the other valve could be partially closed, but not both). Turns out I never used the narrow tires and the rear valve was all I needed for my current setup.
The thing that caught my eye in the photo is the brake actuator push rod. Specifically the bend in it. It sure looks beefy enough so you wouldn't have to worry about a 'collapse' in the bends. However, the offset in the rod will produce a vector that does not allow all of the force at the pedal to be transferred to the booster. Also, assuming that the ends of the rod are parallel to each other with the offset achieved through a kind of lazy 'S' bend, this will produce a side loading of the rod as it enters the booster. This may not be a big deal because of the power assist.
I had the somewhat the same issue with my manual brake setup - the brake push rod from the pedal did not enter the master cylinder exactly in line with the MC's bore. I rigged a trial setup using much the same principle as Lance did, and found that even though the push rod entered the MC at the same angle as the bore, the side loading caused when putting pressure on the rod caused the piston actuating mechanism to not operate smoothly - sometimes you could feel a faint 'catch' in the pedal. I fixed the problem by machining a full span plate shim for the MC mount that changed the mounting angle by the 4 degrees needed to allow the use of a straight push rod entering the MC straight down the bore. My .02.
A great looking project, Lance.