OD of New Pin 18 mm. Length of New Pin 53 mm.
OD of Original Pin 7/16" Length of Original Pin 54 mm. (but not always!)
[Don't forget that conrod little-end eyes are NOT central to their pistons/cylinder bores]
A suggested, possible way forward is to make up aluminium-alloy, or even bronze, bushes as per dimensions in the sketch.
New piston circlips are of dia. 1 mm. wire: their tails would have to be clipped off. This is not a problem to their removal from a piston as handily, pistons have cast-in circlip access slots.
Tolerances:- Between original 'pin and new bushes: "light hand fit".
Between new bushes and piston: "medium hand fit/light push fit".
WARNING:- when fitting aluminium-alloy bushes to piston, ensure that surfaces are lubricated, not dry, to avoid possible cold-welding/galling.
Thermal Expansion Coefficients have been consulted: interference fits are not recommended.