I saw a nice looking 1995 Ford L9000 Aeromax on Iron Planet but the way the truck was built seemed wrong. It had a huge box with front and rear drop axles. Rear ends were 40K but the front axle was only 12K. Seems like the front axle would be a real weak point and defeat the purpose of the drop axles?
It's part of the reason for drop axles. 12/40 standard issue, mainly highway specs, seen drops installed like that, it works. Most on highway air ride suspension is 46K rated and standard for drive axles last 18 years. Problem with adding drops is mounting area/location on frame. Crossmembers are a must have item at axle mounting point.