Ive been researching extensively on improving the capacity of the a15.
I found that datoman 1000 is right to be safe and stay with 77mm for good sense.
I also found another way to go the way that "engine masters" are going for their 850hp 8litre v8 competitions. They are going small bore and long stroke to get the highest and best torque throughout the rev range for the last 3 or so years instead of square bore and oversquare bore engines.
Having said this if you are going to be serious in capacity increases over 1600cc a 90mm e16 stroker crank machined to fit the a15 will be the way with 20mm longer rods (149mm z22 or 152.5 mazda rods).
To achieve this a spacer place (like Jun and MUgen have for the SR20) will have to be made to accomodate the longer rods to help the rod ratio and sleeving the whole assembly with 79mm offset bores or 80mm if possible with a step on the base of the block. A Feral or Jts oval port head will finish the job off and also a Proinjection liguid vapour injection LPG system for economy.
1765cc with 79mm sleeve bores or 1810mm with 80mm offset sleeve bores. With billet sleeves you could also turbo the lot.Youll also need some high quality longer head bolts to torque it all down and the rest of things like SS or copper head gasket, arp rod bolts eg.