Now Mr DatsunSSS, you may well have hit on something that's VERY usefull here

The listing gives two part numbers for the A10 & three for the A12 engine. It's the A10 listing that is of most interest.

In the listings the numbers all begin with 12010, so for simplicity, I will leave this out & just go with the suffix part of the number.

A12 Part No.
-H1001 Standard piston. This is the earliest part number & was superceded from 6/72
-H1061 Not found in my parts book. Is this the flat top GX piston?
-H1011 This is the part number for the piston that superceded the first one on this list in 6/72

I suspect that when ordering pistons, you would add a suffix indicating the required oversize

A10 part numbers, again all with the 12010 prefix.
-18021 This is the third part number, so it would be the second supercession. This would be a standard A10 flat top piston.
-H2301 Not shown in either my B10 or B110 books. Part numbers with the 'H' prefix are normally 1200 model part numbers. Is it possible that this is the 1200 GX flat top piston as all pistons for the A10 engine, at least the ones used in the B10 model, were flat top.

Can anyone shed some more light on these two, as yet, unidentified part numbers?