It is a very unique block, can bolt on old stuff, but won't work with them (due to reverse cooling). This is the Gen II engine, they did a complete redesign, very little is shared, even though related.
LT1 cams can be run in older SB's, but lack mech fuel pump eccentric. And the pin on the front is long, which may interfere with the front cover (I am sure it will) so it will have to be cut down or changed. The LT4 HOT cam was designed on a std blank with mech fuel pump eccentric, but is compatible for all SB's.
The LS1 shares NOTHING parts wise, not even CID. It is a 345 CID engine. Only bore spacing remained the same (probably to save on tooling costs to tools could be modified to work on new blocks/heads, tooling is VERY VERY expensive!)