On a K20A you can bore out to 87mm no problem, but Honda only offers 0.25 mm oversized pistons and rings, so if you want to stick to Honda parts you're limited to 86.25 mm. For some bores 0.25mm is not enough to remove the bore out of round (which can be 0.006" on a stock engine which has had a hard life). K24 engines can't be bored much - Honda has a 87.25 piston/ring, and I think the iron liner looks pretty thin above this.
91 mm would probably be the max on a k24a but you would really need to ask block experts like golden eagle, darton, rs, etc....
Nikos