Hi Craig,
The 4G92 and 4G93 pistons will fit. The wrist pin is 19mm in all of them.
I've spoken to someone who used 6A13 pistons in a 4G93 turbo and it worked but the compression ratio was unusual (can't remember what it was).
However there are many 4G9X series pistons available stock so one of them will likely give a relatively good compression ratio.
As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.
Alternatively you can use spacers to lift the pulley that holds the timing belt between the two heads.
The drawback to all this is that you will need to customize the intake manifold and exhaust manifold (or at least the Y pipe).
Additionally, the MIVEC valves are smaller than the 6A13TT valves (both intake and exhaust). Which mean a far easier, cheaper, straight forward and more powerful option would be to just rebuild a 6A13TT with high compression pistons and use the 6A12 DOHC non MIVEC camshafts (if you really want to remain NA).
If you got to
www.ozvr4.com there is a build thread thread for a 6A13TT MIVEC by user "6A13TT TYPE S":
https://www.ozvr4.com/threads/adams-99- ... vec.13822/
You can see what he did (with plenty of pictures) and he is also active so you can IM him with questions.
If you do find more info in this, do post it back here, perhaps someone in the future will look at it and do his own build.
Another thing to keep in mind is the 6A13 block has a taller deck height so it is unlikely that the stock hood will shut over the engine.
Anyway, as you can see this is doable but the costs keep piling which is why no one has really done this, because in the end there are just cheaper and faster alternatives.
Which state are you in?