The standard piston for 490cc OHV engines in the twenties and 1930 was equivalent to Hepolite's type 2797 - see photo of a New Old Stock one above - but these are hard to find and I don't know of any company making replicas. This one is SOLD
However,a piston equivalent to the Hepolite piston 3478 (with 5/8" pin) was the standard wear for Moore CS1s/ES2s but can equally be used in pre-31 490cc OHV engines, albeit with the possible down-side of a higher compression ratio. So what you may say - just put a plate under the barrel but ... then you may encounter minor problems such as the push rods being a bit too short etc etc.
Photos are attached of a very worn example I still have of one of the 3478 Hepolite products and I heard recently that JP Pistons in Australia are making a replica of this type under their reference 0875. Contact them direct for details, prices etc.