That's a good thing. The sodium filled valves you'll want to pitch in the trash. They have a bad reputation for the stems cracking. Once that happens and moisture gets to the sodium, the stems will explode. Other than that, that is a really heavy duty engine. My 331 is just like it. They have more meat in the heads, hardened valve seat inserts, and if it's the real truck/industrial heads, they flow better than any of the 392 heads ever made. They are every bit as good as the famed "triple nickle" heads on the 354. The block has a pretty strong chance of being an "extended service" block, which means it can be bored MANY times. Most can to at least to and possibly beyond 4". Sonic test of course to be sure. It might be worth looking into.
