An unbalanced engine will not last, I find the first problems seem to be oil leaks (front seal or rear seal), oil pressure will start to drop off as the main bearings get worked by the unbalance, after that the end is near. 

I'm not that familiar with all the Y-Blocks but one of my racing engines has a nuetral balanced crankshaft so as long all the piston/rods/bearings/rings weigh the same I'm good. (yes rods are evenly balanced). We just completed our scrub dirt track engine with different Pistons and 2 replacement rods and the crank was quite about out with new combined bob weight. Our machine shop does not regrind cranks but does everything else. He goes a lot farther when doing race engines but surpasses factory specs for any street engine. I, like most here, will say even if it takes alittle more time, balance your engine; you will never be sorry. Good Luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

See if this link to a past thread regarding oem piston weights helps.
http://forums.y-blocksforever.com/FindPost59692.aspx

Lorena, Texas (South of Waco)

Thanks Ted, I found the OEM weight. I was also just wondering why a replacement piston manufacturer would make a piston 63 grams heavier like the original poster asked about?

Just a little feed back on this subject. The Y I am rebuilding is just a stock, non racing, 292 that is .060 over. I just have a set of cheap Sealed Power/Speed Pro pistons and weighed them this weekend, all were within + - 1.5 grams of the OEM weights..