They may be aftermarket pistons, manufacturer unknown.

The link is to some engine parts retailer. I dunno how they are, somewhere in New Zealand perhaps.

What is that place? Details are sparse at best...

After cleaning the top of the pistons I found the number:9038P Does that ring any bells with anyone?

If that's the case then your compression ratio is even less than you thought because the swept volume of the cylinder[s] is less than you calculated, .. by approximately 8%

I just checked the stroke... Only 70mm. It's an A12 Crankshaft In the A14 block... There's my missing compression.

Let's take Dodgeman's formula.

R squared x Pi x L [x number of cylinders if you want whole of engine displacement] divided by 1000.

76.3 ^2 * 3.1415 * 77 / 1000 = 1408 cc

Now take the combustion chamber:

29cc cylinder head chamber + 3cc Nismo 0.8 gasket + 4cc dish = 36cc

1408/4 / 36 = 9.78, but that's without considering deck height. 3mm seems a little too much deck height?

Well... Hopefully my math is off. Based on the measurements and the formula I came across, with these pistons and an H89 head, the compression ratio works out to 8.08:1???!! That can't be right can it!?
Bore: 76.3mm
Stroke: 77mm
CChamber Volume: 30cc
Gasket Thickness: .8mm
Piston Dish: 2cc
Above Deck: 3mm
or Above Piston Volume: 15.717cc
I used a gasket Bore size of 79mm because that's all I could find but I assume there is a more appropriate size?
Any thoughts anyone?

I rebuilt an A14 engine for a workmate back in the 1980's & I bought two new [genuine] pistons to replace a couple of damaged items.

The new pistons had a much smaller dish than the originals & it became necessary to buy two more to match. I have no idea of the origin of the A14 & no idea what model that the new pistons were intended for but clearly there are a number of different piston & cylinder head combinations.

I haven't measured them yet, but just eyeballing this dish seems to be only 1mm deep, possibly 2 at the most....