I'm not a Sanger guru so take this with a grain of salt, but here's what I know.
Sanger had some intakes done in the factory that were machined for a ride plate, but not for a shoe. If you wanted to add a shoe to this setup, ideally you would pull the intake out of the boat have it machined to accept a shoe and the rideplate would fit into the rear of the shoe. Do some searches for pictures of shoes and rideplates on this forum and you'll find some good examples.
As for the other intake that doesn't have the macine work for the ride plate done, it would require the same amount of work with the exception being that you'd also have to fabricate the cradle or turnbuckles to support the plate at the rear.
In terms of how your Sanger is made.... Thats a loaded question. Everyone has their preferences and even some of the best builders have probably let one or two bastard layups slip out the doors at some point; either due to bad materials or someone being asleep at the wheel. Folks that have sangers tend to like em, but then again, most folks don't really talk crap about stuff they own. If your buddy's boat is a full stringer deal, there aren't any cracks in the glass, and it seems structurally sound, it's probably fine. There are other makes of hull that will go faster with the same HP, but thats not the end all be all of what makes a boat a keeper. If he's happy with it, and its in good shape, its no bigger hole to throw money into than the rest of our boats.
Chris