they would have to be custom... BUT... if you do the flange with a 'spigot' type mount that would be a medium press fit into the D44 bearing bore... and then bolt (studs) back through the backing plate flange... i think it would easily be as strong as the welded setup they did... basically that is the same type of mounting as the D44 spindles, it 'spigots' into the knuckle (or flange for the rear floater)
if you were still concerned about strength, you could make a thick flange to weld to the back of the original D44 backing plate flange, make it 2 pieces and weld it all to the tube, to spread the bending load back into the tube further.
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