You all have gone through my same thought process. I will address every point, since you all understand what the idea is:
The links are made from 2 different C-channels and each riveted with two 1/8" aluminum pop rivets. The problem is that this is very weak and time-consuming. I have not considered screws, and I will try it. What size: 4-40 or 6-32? Nylon insert locknuts, or tapped holes?
To drive the tracks I am hand filing 2 drive sprockets out of 1/8" aluminum sheet, distanced apart using standoffs. This sprocket engages the ends of the 3/16" steel pins.
I was thinking about the standard attachment chain, but its would be much heavier if I used 2 chains. However, I might scrounge around and find some other material that would work for small rollers traction rollers to be used on just one chain.
Many people have suggested using waterjets or CNC mills. Why does a waterjet or CNC mill seem right for this project? Do you fabricate a bar with the correct profile, or do you cut individual links?
I do have a mill: my 14" Nicholson mill file. Ha, ha! Yes, do file my own #25 and #35 sprockets out of aluminum, and yes, i Am CrAzY. No need to buy those IFI sprockets! 
Sorry about that. Just a random fit of insanity.