This may sound weird but I don`t remember making any changes to the driveshaft of my 53 F100 when I replaced the original rear axle with a 9'' from a 67 F100 many yrs ago. Maybe my memory has completely failed me on that.

 

It is the stock rear axle (Dana 44 ?) with a sheet metal rear cover.

I sounds like the gear change would be the simplest and perhaps least expensive way to go. Where would I get a carrier for a 56 and earlier rear for the numerically lower gears? Mine will only work for 3.92 and up... is the internals of this diffused for any other applications (newer?)

 

I can't say on a '53, but on the BonusBuilts it works out to about an inch and a half longer driveshaft needed. The 9" has a shorter snout and the pinion seems to be a little lower, plus the larger tube diameter pushes it all down slightly. If you flipped the axle you would likely have to shorten it.

 

Number Dummy will be along to set me straight but let me give it to you from the garage side of this/

Yes you will need a 3.73 or lower carrier

If you had the carrier all you need to do is find a mid 70s f150 with a 300 6 cyl and auto tran. This set up say from a 77 will have a dana 44 with 2.72 gears

I have personally done this swap, but my 56 had the 3.73 carrier already, All I used was the ring and pinion from the mid 70s dana and reused my axle side gears as the axle spline counts are different from the old to the newer rear end.

between the 2 rear ends I had enough shims to set up properly

I currently have the 2.72 set up in the truck, but I still have a 3.92 rear end that when I want to do a parade etc I swap them out, takes me about an hour now as I have done it several times. I swap the entire axle, not just the gears

The 3,73 ratio rear was an option for the 56 f100;s and its a tough one to find.

I believe they sell new ones (carriers) but then its pricey.

Also, you wouldn't want to use the whole rear end housing from the 76 77 ford truck as its wider FYI

Also you cant use the later 76-77 carrier as the axle side gear do not fit into the machine surfaces correctly. I;m sure I have forgotten something as I did this swap long before the internet

 

Here is a good source for information and parts
Diff Wizard