I wouldn't follow any of the advice on the the 2x6 equipped aluminum V bottom you posted. It's ridiculously overbuilt, so much so it'll need another 20 HP just to do the same speed it did previously and this also dramatically lowers the boat's stability and capacity.
The other one at least uses 2x2's which are still more than you need, but a fraction of the weight of the clown using 2x6's. Unfortunately, he still used 3/4" plywood decking panels. I always wonder what they're thinking this needs to hold up, a full size fridge, full of beer? Of course he also uses carpet over the wood, which is a God send to people like me in terms of future work, because carpet on wood is a guarantee that you'll be back to have it replaced. His other "upgrades" are good ideas.
To build a casting deck you only need an aft bulkhead, some 1x2 stringers and some 3/8" plywood to fit the deck space. On an aluminum boat you don't drill through the side of the boat, into frames. The frames and other support structure (stringers, cleats, etc.) are attach (screwed) to existing structural elements, like the chine log, bilge stringers, etc. These are riveted or welded to the aluminum hull shell, so an appropriately sized screw doesn't penetrate the hull, just the stuff inside it. I just did this to an old 14' tinny and used a couple of 8' - 1x2's and about 2/3's a sheet of plywood. I added maybe 20 pounds to the boat total.
Most of the time, if you make a template for the casting deck, running from chine log to chine log, the plywood will neatly just lay there, maybe with a few screws to insure it stays put. The trailing edge will need some support, so this is where you put a bulkhead, which can have a hole (or two) cut in it so it's a ring frame instead. Screw a 1x2 along the top of this 3/8" plywood bulkhead, so the decking plywood has something to land on. Additionally, if any of your well fed friends will join you on this deck, you'll want a few longitudinal stringers, notched into the ring frame. These tie the casting deck plywood to the ring frame once it's all screwed down. Space these fore and aft stringers on 12" - 14" centers and let them land on the chine log. They're just stiffeners so the plywood feels firm under foot.
Instead of carpet, consider truck bed liner or a "FlexSeal" coating. It's tougher, waterproof, has much better under wet foot traction and can be repainted and pressure washed when the time comes.
I fix these "tinnies" all the time and I usually pull out a lot more wood than I put in. The boat is rated for what it's rated for and you can screw all the 2x6's to the transom you want, but this doesn't make it a good idea or even legal. There's a formula for figuring out how much HP you can toss at this puppy and going over this sounds like fun, but odds are I'll read about you in the paper some day (We read about people finding a way to drown themselves in boats regularly where I live). Besides, you don't want to take that boat much over the mid 30's anyway. The hull form is a type that will beat you (and the boat) to death are speeds higher than this. Tell me the boat's length, transom height and width are and I'll tell you how much you can safely put on her butt.
