On spring hangers, nothing special.
Just a piece of ordinary mild sheet steel (1/8" or 3/16"?). Available at any shop that sells misc. metals. Sometimes these shops have a shelf or bin of scrap pieces that can be had for cheap. Could cut with a hacksaw or cutoff wheel in an angle grinder (or a few other methods) to match the existing dimension. The steel shop should also be able to cut a square piece for you on a chop saw or band saw. Use a file to smooth off the cuts and drill holes to suit. Course, some welding required to frame.
Spring hangers are sold separately like at easternmarine.com here for example.
https://www.easternmarine.com/Leaf-S...Hangers-Seats/
If you want simplest/fastest, go to a frame and axle shop.
Linear Mode
