im going to take my block to the machine shop in a few days but i want to make sure its a standard bore first. i heard that the pistons say the size on top but these ones dont. i looked all over the pistons and cant find anything saying what size they are. they have GM stamped on the inside of the piston skirt. does that mean they are the original pistons?
thanks

Most if not all aftermarket pistons will have the over bore size stampped on the crown.

If they don't then a good 90% of the time, it means they are stock.

Being you found GM stamped in them, I would say they are stock bore, stock pistons

I second that!

Here is a handy tool (dial caliper) to have for situations like this:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=5647

At $9.99 you can't beat the price. These are not accurate enough for honing cylinders or checking bearing clearance, but when "close" is good enough they work like a charm. BTW HF charges like $9.00 handling on all orders so if you order from them make sure you put in one big order, or go together with a friend.