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A lot of us have put larger 11" x 2 1/4" front Hudson brakes from newer Hornet & Commodore (Backing plates, lining, and Drums) on older 1937 to 1947 Hudson's to improve stopping ability. Everything is interchangeable except a bearing from the '40 needs to be inserted in the later hub, with an 1/8" spacer washer, but none of this apply's to your install except know the Spindle Bolt Pattern from the '40 is the same as Scarebird newer '48 -'54 Hudson Listings.
That said, I don't see why the Scarebird bracket Kit cant be installed on your spindle since uses your '40 Hubs & bearings. Just follow their instruction for Rotor, Calipers, etc.
Only install if you have seat belt.Whats the reason. Brakes are too good for no sest belts?Thanks for your pics about PB. Will take a power booster underfloor to hold the original pedal
If i connect the hose i will report
I have only one piston. If you see the mechanical movement inside then the brake cant bent the mounting plate because the disc is between the brake pads. If the piston under pressure the outside pad comes with mechanical movement to the outside of the disc. Its a swimming caliper. Only important are the screws that hold the caliper on the plate.