I like the ruffstuff perches, one of the few places with narrow ons that are also long, not for a trailer axle.
The ones I needed were to fit about a 3-5/8” tube, they wouldn’t custom make them at the time so I ordered some for smaller tube and machined the radius to suit.
Wouldn’t weld a gap, get them to fit real tight before welding in place.
Also, don’t forget to carefully measure and set pinion angle before welding spring perches on.
Tech Tip with excellent resources linked here.
https://www.stovebolt.com/techtips/driveline/setup/index.html