I'm with Chris, I wouldn't want to see any kind of a modern axle hanging below the bed of my Model A pickup, which has the most visibility of any body style. A thouroughly rebuilt A rear axle can live very comfortably behind a stock or typically modified flathead 8. Probably the biggest factor in it's lifespan is the driver and how he/she "drives". There are a wide variety of gear ratio's available new, so they can be set up to meet your requirements.
If you desire a later, V8-era rear axle then a '33-'34 could be a good option as they offer a stronger design and are essentially the same track-width as an A rear so your tires will stay centered in the fenders. The only down-side to the '33-'34 is that they are *typically* a 4.11 ratio and new, taller ratio's aren't available for these two years. Original 3.54 gears were available but are next to impossible to find these days. (Although ring & pinion sets for '35 and later can be modified to work, this was done to get 3.54 gears in my Dad's '34 Roadster.) However, if you are planning an open drive set-up because a 5 speed transmission is going to be used, like a T5, then the 4:11 gear would offer great around town driving and the overdrive will drop the engine RPM to a more than comfortable speed on the highway.
If you wanted to further fortify the axle, the Hot Rod Works could set it up with 8/9" style push-in axles and bearings which can still work with early Ford or Lincoln hydraulic brakes to keep the appearance traditional.
You would also have to install spring shackle brackets on top of the axle tubes to mimic the Model A arrangement, but you would have to do this with an 8" too. And, like said above, using a Model T spring with reversed eyes will net you about a 3" drop out back and you could probably get even more by de-arching the spring.
