this is off another forum and the info is really good.
You could look at some +30 2.5 HSC or 4.2 Vee-Eight replacement pistons, which are taller than the stock 250 items by over 50 thou. They are dished quite a large amount. Then look at the 6.00" rods from a couple of wrecked Taurus or Tempo 2.5's. Remove nothing from the head, and get a nice thick gasket of about 50 to 80 thou. Doing this will help correct all the things that hurt performance, fuel economy, strength, and engine design restraints. It's soooo rare to be able to do any rod swap on any engine without getting special expensive bits. The 250 is a walk in the park, because the 2.5 OHV engine is just a scaled I6 with a shorter stroke crank and about 17 years worth of extra developement.
Then spend some time chasing suppliers. 4-cyl stuff is always tougher than I6 gear. The fours vibrate lots more, rev to a much higher RPM, produce more power per cylinder, carry more load per cylinder than a six, and suffer more detonation than a I6 was ever designed for.
you want 2.5L HSC rods as recommended by xtaxi... but the 2.3L HSC flat tops have the 1.5" compression height (perfect) the 2.5L HSC pistons are a tad taller.
