I have a set of KB 257 (.250 dome) and 14092359 heads, all I could find about the heads was (14092359...86-90...oval...OPEN...366T, 427T, Marked "HiPerf")so I "assumed" that a .250 dome would fit into an open chamber head without problems...BUT it seems that my heads are more like "semi open" they're around 107-110cc :eek:

Now the back side of my dome (where the sparkplug relief is) is hitting my chamber on my heads
My question is do you guys think it's safe to use a die grinder to remove say.... .20 to .40 thou off the back side of the chamber? I realise there is a water jacket back there but I can stick my finger inside and it feels like the walls are over a quarter inch thick

Has been done many times. I'd check with a shop if possible for how much you can cut where.
You could swap pistons to TRW forged 2465/2x49. Which ever one it is for closed chamber heads.
Same CR.

The TRW 2465 are open chamber pistons and the 2349 are closed chamber pistons. The 2349 will work with both sytle of heads and will provide about .3 more cr than the 2465 in the same cc head.

Whoops...Forgot to mention that graemlins/clonk.gif
I've been to all the "so called machine shops" in my little hell hole of a town and nobody will touch them because it's considered "Performance" work and they don't do performance machining. Nor could they give me any advice really...everyone tells me "I've never heard of that before" or "You need to buy either new heads or new pistons" I just paid big bucks to have my rotating assembly balanced, and I have the owners of the local speedshops drooling over me like a piece of meat in front of a pack of hungry dogs cause they think that they can sell me heads.

Basically what I'm saying is that nobody around my town really knows too much about this kinda stuff. But I coulda swore that I had seen something about someone enlarging the chambers in their heads.

I think that you would be better off keeping the pistons and finding a set of 049s or 781s. I have K/B 257s with a set of 781s. The truck heads probably have the smaller ports and are not quite as good of a performance head.

I take it you are putting the motor together. I don't want to sound ignorant BUT, When I was putting my big block together I used a crane double roller chain set. I always used comp before. When I got it together and turned the motor I would have contact. I a friend come over, more experience than me. he looked it over said pistons had to big of dome, got new pitons, same thing, well i finally figured it out, it seems that this crane crank gear has little A's, R's & little ones, I had the crank gear on wrong, I have close chamber heads so it made a big difference when it was on there right and i had good clearance. Just something to maybe look at, I was dazed and confused for about a week with this, work all day, come home and put the motor together wrong. Should have had a beer I guess.

I ran into the same problem with my 468, same .250" domed pistons, but didn't check into the heads as thorough as I should have. Edelbrock oval port heads are 109 cc, rectangle port heads are 120cc. Missed that little detail. I didn't feel like selling off new parts, and buying more. Worked the chambers myself, came out good. I ended up with about .060" clearance to the domes on all of the cylinders, which is sufficient with steel rods from what I researched.

http://www.chevelles.com/showroom/Cameano/chamber.jpg

Is that .60 with or without the gasket?
Your chambers look VERY similar to what I have now.
I Started to grind today and only got one chamber into shape and 3 others pretty close, I'll finish them up later in the week.
How thick do you figure your walls are?
Thanks for the picture and info/opinions guys graemlins/beers.gif

.060" with the gasket I'm using. I used a depth micrometer to get it right, and clay on each piston to check final side clearances. You should check each cylinder on the engine, and do one at a time.