Pato as far as I know the two guards are very similar and with a bit of work should be interchangeable.
The M20 guard has a bracket rivetted to it that holds the battery box/ oil tank and the plate they bolt to, you would need to remove this bracket and weld up the holes. The A type guard has two straps that hold it to the frame at the bottom front, only need to drill two holes to sort that.
I have never tried to fit a M20 plunger guard to a plunger A but I am fairly sure you could.
