are you on crack? that wont get you 250. besides the fact that no one makes 81.2mm pistons (theres 81.25 or 81.5), you wont make 250 hp with a 1.8l. that setup would probably make like 200ish. and you wont get 250 with 2-3g i have about 5-6 grand into my motor (1.8l gsr stroke) and it puts down like 215 at 11.5 compression. although there were some things i did for the sake of rules rather then what made the most power.
if you want 250, you are looking at at least upping to a 2.0L block, high compression, good cams (gonna need bigger then ITR cams, skunk2 pro1's or even pro2's). good portwork/valve job GOOD header. etc. and its gonna cost a lot.