Oh, I don't have a machine shop, I work in a tool and die shop so I have access to the machines but I wish I did have a mill and lathe at home.
I build all sort of stuff to get myself into trouble LOL!
Those Armortech models are beautiful but they cost about 8k to 10k dollars here for the ones with all the options.
I don't think a 1/6th scale model of the LVT would be any harder to build than the one you've already done and some of it would probably be easier.
Large scale means details like exposed nuts and bolts are much simpler to do.
But there are drawbacks, the main one is where to store the thing once you get it built, if you have the space then the larger scale isn't a problem.
As to plans, do what I did, take a set of 3 or 4 view drawings, the ones you used to build your current model for instance, to a printing shop where they enlarge blueprints for houses.
It should be relatively simple to find a shop that does this and have them enlarge the drawings.
I found these if they will be of any help to you.
link link There's some more drawing there dealing with those Amtanks plus Amtracks.
Not sure how much trouble the WWII US TD's would be, guess it would require taking a close look at the hull type.
Some of them were welded hull which usually means simple enough shapes to make scratch building possible with a minimum amount of headaches.
In fact, here's a fair set of drawings for the British M-10 ,with the 17 pounder, which looks to be a welded hull machine rather than cast.
M-10There's drawings at that site for most any armored vehicle you might take a fancy to.
No GI Joes, there's a series called Soldiers of the World that have armored crew members from just about every nation during the war and they work very well for this.
I'm not sure I'd do an unbuttoned model though because I'm not planning on detailing the interior.
WOLF