If this were my pedal, I would grab a couple of steel crankarms from my cottered collection, douse the threads with anti-seize and forcefully run the pedal spindle in, using back-and-forth action.
The anti-seize is important, lest the metals gall (cold-weld) against each other, and which is still possible if high enough turning speed is used.
Back it out and clean/inspect if the turning starts to feel crunchy.

Hoping that this will re-shape the spindle threads enough to prevent the spindle threads from damaging the destination alloy crankarm.

I've had Shimano pedals which went in tight into older Campagnolo cranks, had to back-and-forth them in to assure that I wasn't going to shear threads or burst the pedal eye.

There are sizing differences between ostensibly identically-threaded parts like taps, pedals and crankarms, so running one or two different taps through the alloy pedal eye might ease the fit.