Anybody break a stock block, if so at what hp?

This has my interest, I'm in a similar situation.. I bought a 340 .060 over complete and love nitrous. The motor was such a deal I could not pass it up. I sprayed a stock cast crank , stock rods and rod bolts 318 last year and ran 10's. Held up fine made about 10 passes..

I would love to hit this motor with a 250 but I'm a little nervous of the .060 over. I'm curious to what your machinest said about the thick walls.. I have a 73 block also.. Is the last digit on your block a -1? ( 340-1) I'm trying to find out about the core shift talked about and since he said yours is so good I was wondering.
Nice looking motor!