A15 is the best, unless you are looking at getting by laws by using an A14 so then just use the A15 internals and sump or counterweights smack the sides of A14 sump.
Offset sleeved to 83mm using ca18de pistons and have the tops machined for valve clearances and to suit combustion chambers. Probably best use ca18det pistons for 10.5:1 max comp by using one of Pjz Gx head he has advertised for sale cheaply.
Offset stroke the 82mm crank to 83mm and you have 1796cc or just 1775cc stock.
Custom head gasket from AAA gaskets in composite material are good one off units.
You might need to o-ring the block for that extra reliability.

1796cc with 41mm quad bike carbs would be a mad little monster.