A18 really but yes the a16 would be easier and cheaper.
However imagine 80 or 81mm bores, 42mm inlet valves,
33mm exhaust valves and the gas velocity of the oval
ports with the extra 300cc over stock 1500cc.

edit: just found out that a full C sleeve is an easier option
at $500 dollars in and out, this is Ultrasonic tested, full
cemented and shouldered sleeves.
However I asked about 80mm sleeves not 81mm as there is probably
not enough material or space for 81mm sleeved bores?

this would mean 80mm bores x 87mm stroke : 1749cc so A17 :)