I found a set of those 65.5 mm pistons cheap on eBay so I had to buy them.
For my K6 old 836 cylinder with wide clearances.
The sleeves sticking out in the cases are even thinner now, 1.25mm.
I think Wiseco 67.5mm pistons in CycleX stepped sleeves also are 1.25mm. A popular set CycleX sold.
(I should remember since I have a cylinder with those sleeves with JE 67mm 890cc I think has 1.5mm thick sleeves where it enter the case.)
The guys in the shop that bored them looked worried before the job, if sleeves could crack. But it went out well.
Same shop bored that cylinder for 836 late 1983
I have not used that set yet.
I made sure to bore a few cylinders while that shop near me still could do it. The mechanic is +70 years old.
The good not much used RC 836 pistons got a cylinder to bore too.
But your pistons are forged JE 65mm (836), a better piston than the old style CycleX 65.5mm piston (849cc) for a much lower price.
They charged $250US for a set when they had them in stock if I renember correctly.