In reply to your earlier question regarding availability of Pistons. New old stock Ariel pistons are not easy to find these days, not impossible but getting harder to find, you could try Draganfly but they are likely to try and sell you Suzuki pistons straight off, at least thats the response I got even though I specifically asked for availability of Ariel pistons, however there is one major supplier I know of for Vintage Engine parts in general that stock Ariel Leader pistons, they are not new old stock but newly remanufactured pistons but having used them over the years I can vouch for their quality, They are PHC Ariel pistons, I believe the PHC stands for Peter Hepworth Components and originally they were manufactured in Italy. (dont know whether they still are)
The supplier is F W Thornton of Wellington Shropshire http://www.fwthornton.co.uk
. You can view their stock on-line and they supply various oversize pistons for the Leader engine.
Thats the good news, the not so good news is the price, last time I looked they were £87 each but at least you get the piston, rings and gudgeon pin.
That said I see someone is advertising a pair of new old stock Ariel +020 oversize pistons on ebay for asking price of £200 a bit optimistic I think but an indication of where we are heading these days with the prices of spares....
The alternative of course is to buy the much cheaper reproduction Suzuki GT250 X7 pistons (genuine Suzuki pistons are not cheap when you can find them) but this does mean you have to buy and fit a new pair of little end bushes for the rods to cater for the smaller diameter pin on the Suzuki pistons, this of course entails having to remove the old Ariel sized bushes with suitable extractor bolt set, fit new little end bushes and reamer them to size that might entail having to purchase a reamer (available via ebay) if you cannot borrow one. (that said if your engine has the Death Rattle, and I like many others have had that on my engines you might find that the little end bushes are worn to such an extent you will have to replace them anyway involving the same amount of work).
One more thing I will mention regarding the Suzuki pistons, they are shorter in height above the gudgeon pin compared to Ariel pistons this means you lose out on a bit of compression, I have the tops of the barrels skimmed to restore compression although a lot of owners just fit and ride and probably find the engine pulls just as well without the need for the barrel to be skimmed. .
Hope the above helps in some way.