I "had" A 350 matching numbers 350 in my 69 lemans, after a rebuild, other than .030 over it was stock on the bottom, I ran cast pistons, torker intake, 068 grind cam, 650 Holley, street stall, TH400, stock 47 heads, rockers etc. Found number 4 cylinder had a crack. As I build a 400 I want to make sure it does not happen again. I know it did not freeze over the winter nor did I notice any detonation. I do bracket race the car with a best 13:44 @ 100.47 mph, and was very inconsistant.

Anyone have any input from anyone would greatly be appreciated. Mike  

There are two basics to build(rebuilding) engines.  1.) Do the best you can with advice from experts(books written by winners)  2.)Even if you do sometimes things go wrong.
Cracks are caused by a higher stress than the metal can withstand.  It may be because of an off-center casting core or a casting flaw that created a stress-riser (a defect concentrates the stress) or it could be caused by and incorrect assembly job.

Build the engine to specifications.  Use the right torque settings on bolts that have had the threads cleaned.  Make sure your coolant is filled and bubble free.  Pay attention to the basics.  

I have seen cracks in the cylinder caused  by inproper clearance of the pistons.  

Thanks for the input, I will be sure to triple check everything this time, this was the first time I ever used cast pistons on an over bore before so I was a little suspect of that, the coolant could be a problem as it is not allowed at the track, one again thanks.  Mike