While the piston is out and in hand , you might consider installing a compression pin .
I pinned the piston of my '57 Simplex using 1/4" long x 3/32" wide compression pins .
I drilled the landings to a depth of about 5/32" . The pins had to be driven in , so it's unlikely that much , if any, outward drift will happen . I used a jewelers square file to square the outer end of the pins and the ring ends , which needed relieving to fit the pins . Then , they were 'good for service' .
That was 5 years ago . Those pins haven't moved an iota , since . ;)