0ver Boring a LA 318, how much is poss for more cubes ?

I welcome all your suggestions, I am trying to plan/work out a budget performance build. How far can you safely over bore the LA 318. I would love to simply get my hands on a 340 or even a short block but alas they are as scarce here as kangaroos in the South Pole!
As I'm in OZ we do not have the scope of performance parts availability as you Guys n Gals are lucky to have in the States. Importing parts is killed by shipping, often costing more than the actual part itself!
Stroker kits are...

0ver Boring a LA 318, how much is poss for more cubes ?
Author: Dodgy Dick