You don't swap to 9" tubes you have to pull the old tubes and replace them with a thicker wall tube. Some people claim you can't pull them out. I proved them wrong a couple months ago. I have a piece of 3" OD seamless tubing I'm going to put back in the center section this spring when I have all the pieces together.
The strongest housing on a Ford 9" is the fabricated housing. They made several styles of housings.
67-73 Mustang/Cougar - light duty, thinnest housing material, small axle bearings, 28 and 31 splines
57-68 passenger car and 1/2 ton truck - medium duty, stronger than Mustang type, 28 and 31 splines
Ranchero/Torino - heavy duty thick wall housing, 3.25 inch diameter axle tubes with flat tops
69-77 Galaxies (coils), Lincolns (coils), and late pickups (leaf)- 3.25 inch diameter all the way to the backing plate, coil housings have upper control arm mount
These are the ends I used. They use the GM style brakes and axle offset of2.75, but they use the Ford style press on bearing with a retainer. I didn't use the retainer because I added disk brakes at the same time. They act as the retainer. Much better than a C-clip eliminators are.
Part # 7900 - Small GM Car Housing Ends (uses 9" Ford large bearing & non c-clip axles)
Cutting the old ends off and the rear to the correct length.
Matching up the new ends for fit
Center section after my Dad welded the tubes and center section togther
Doughnuts used for the alignment bar
Doughnuts in the center section
Passenger side shock mount, crossmember and lowering block
Passenger side final mockup
Rear shock mount
Some final pictures