Just wondering whats the max size bore you can do to an A14 and what would be an advisable size to do?. As pisons 1,2 & 3,4 dont have a huge amount of room between them.

Boring A14? A14's are never boring.
As for the size of the cylinders, they will obviously go to the third oversize of 1.5mm, which makes ti 77.5mm. After that, it depends on piston availability, your willingness to sleve the block if necessary [if walls get a bit thin] & finally of course, how much material is left between the cylinders to support a head gasket.
If these blocks are anything like the 1200, you should be safe at 79mm.
Chris

which is a bore of how many thou?

If you go to the third oversize the bore size is 77.5mm which equals 3.051 thou.
Source your pistons first then bore the block to suit.

1.5mm oversize is .060" (sixty thou)

77.5mm is indeed 3.051", but that's inches not thousandths (of inches)