It'd be difficult to use an air suspension seat on the driver's side of a 416 because of the small clearance between the driver's thigh and the bottom of the steering wheel. You can, though, install a spring suspended seat like the Cobra I had in Camper Mog.
For the passenger's side, I installed an extremely plush, air suspended, over-the-road trucker's seat with lumber support, thigh extensions, etc. I got this from the Freightliner Surplus store in North Portland before it closed (sniffle) for $400. I needed to have to reinstalled on a low-profile base, however.
I've no way to know if it would have fit in a stock 416 cab. Camper Mog's custom cab had much more legroom and no height restrictions for the passenger's head.