bit of work but what about removing the pistons and machining the crowns down so the pistons are flat across the top, increasing squish clearance?

Run a head saver shim. I have the part numbers for them somewhere.

One thing to remember is the largest clearance in any engine is squish clearance,this is because of rod stretch.
All engines you must remember are not a static machine,that is why we use hone plates to take into account stress when bolted up,cam ground pistons so they grow to be round at the manufacturers desired running temperature,hence why you run manufacturers rated temperature thermostats etc.
Generally when building engines the minimum squish clearance I will use is 35 thou any less invited trouble with piston valve or chamber clearance.Conrods will actually stretch more than you realise under running conditions.

With a top fuel Keith Black for example having built them we had to allow for an increase in height of a full 10mm when adjusting the blower belt as the engine grows that much taller between Cold and running temps.
Bottom line as stated earlier when you calculate head gasket thickness etc rarely can you exceed 15 thou out the top with most engines unless the head is relieved to take that into account.You may be able to run standard low comp pistons with a deep dish and the crown milled shorter,many modern engines run the ring pack a lot higher than early engines when manufacturers are chasing minimising the dead area above the rings trying to pass ever more stringent emmisions standards so it is an option.

Hmmm, I will measure the stroke tomorrow. However it seems the block has been milled 4mm so maybe it's just an A14 crank.

you sure its not a a14 with a15 crank, a14 rods and pistons?? this is the 'cheap' way of doin a a15 flat top motor ive been told.

Do you have access to a dial indicator, if so you can measure the lift via a push rod and a degree wheel off the crank can tell you duration. Dont forget to take into account the rocker arm ratio to calculate the final lift amount.

Valve seats are original as far as I know.

Cam I do not know as it is a used A14 short block that edp gave me. I will try to contact the guy who built it tomorrow. Apparently a 1200 racer who sold all his 1200 stuff to edp.

Is 0.030 inch the minimum piston-to-head clearance for A-series cast pistons?

Have the valve seats been recut at any stage, You may have a little extra margin to play with if they have.. Which cam are you using, something with modest lift and duration I assume. A head shim could also be an option as well.

0.025 inch pop-up = 0.635 mm

Standard head gasket is 1.2 mm thick uncompressed which is 0.047 inch. That leaves not enough clearance if I calculated correctly.
1.2mm - 0.635 = 0.565 mm = 0.022 inch (need 0.030 to be safe)

The open chamber heads have a 2.5 mm counterbore, so that would work.

Now what would the Compression Ratio be?

Thanks! GX Comp head is closed chamber with the large (A14 size) valves, so any of my heads should work then. It will be a squishy squich!

sorry I have no DCOE parts. I'm a mikuni man.