Andy Dingley wrote
wrote

The issue will be obtaining a suitable shunt ... assuming
I use a 1 ohm shunt, anybody made one of these ?

You don't "make" a shunt,

You can do, most obviously from whatever suitable wire is handy.

you find or acquire one, then you calibrate it, according
to whatever resistance it turned out to have.

Otherwise it's a right sod of a job to adjust one.

Not if you make one out of suitable wire,
you just vary the length of wire used.

If you want one calibrated to give easy round
numbers as an output, just use a potentiometer
across its output. If your display meter has a
modern high impedance, this is easy.