The bars are listed as "6061 Aluminum" in the Fastenal catalog. One bar has writing on it saying "6061-T6511"
You have 6061 (alloy), T6 temper (peak strength), 511 (which is stress relieved by stretching the plate). This should work good for you. It is not stress free, but it is more stable than if it did not have the stress relief. Basically by stretching a couple percent, you align all the residual stresses so you minimze distortion.
I would use a heavier anti-sieze than the light oil you are using. Mostly so it is effective against corrosion. Torquing should just stretch the bolt, not cause much distortion of the part. Unless you actually pull threads out of the aluminum. By design, bolts are stretched when properly loaded. The trick is to stretch the right amount. Hence the rod bolt micrometers used as an example of a very critical fastener. Torque is always a very rough indicator of stretch. But it is the easiest and fiarly repeatable method. But lubricants, coatings, metal finish, galling, and other factors all contribute to torque vs stretch. I do not know the proper torque setting to use vs your dry, but I think you could go with a lower grade bolt torque, such as grade 5 dry torque for a grade 8 with lube.
If you really want better results, a threaded insert in the aluminum is better than direct threads in the aluminum. The big problem you have is that the aluminum will corrode in the threaded hole and that is what make disassembly difficult. That is why I said use anti-sieze. I do not recommend oil.