By the looks of the overall finish as well as the cross-section when you cut through it, it looks like he uses 5083 aluminum alloy, which isn't even in the T6 class of alloys. 5083 is not recommended for any type of structural use, and is commonly used as a fascia material to cover up other structural materials, especially since 5083 polishes fairly well, after some pretty aggressive sanding and multiple polishing compounds.
Also 5083 is FAR cheaper to buy than 6061-T6, and FAR easier to machine/mill than 6061-T6, since it is so soft and doesn't wear out end-mills and other milling bits & tools as quickly. As soon as I can find a chemist willing to do the required alchemy tests (maybe the local college tech department, etc.), I will confirm for sure what alloy Dan uses.
Bottom line, if you do anything more than just run the truck up and down the street, Dan's chassis juat isn't for you...you need to use one of the many other chassis currently available. If you can find one, the Gorillamaxx Revo chassis (either carbon-fiber or aluminum) is your best bet, followed extremely closely buy the Vantage Racing carbon-fiber chassis, or just scratch build a full chassis yourself, since you are so good at scratch building things. Check out
this scratch-built chassis a guy made (it's for the 1/16 E-Revo, but you get the idea)...