piston identification on 273

I wouldn't be thrilled about a 40 mil over-bore. Usually blocks are bored to re-use them, not for more displacement. Yours is probably at the limit and can't be bored again, unless there are 0.060 pistons for a 273. Anyway, re-boring a 273 is usually out of love because the price of a new piston set is much higher that later small blocks, so it is usually more cost-effective to switch to one of those, plus better parts availability.