There will be no problems with the switch as you are only changing the block and not the ex. or intake manifolds. If you have not purchased the block yet consider a f54 block instead, it will give you more compression. Add a performance cam to your set up and you should feel the difference.
When I bought my 260Z, the original owner had blown the engine (idiot drove it without oil!). He put a new engine in it, it was an L28 with N42 head. He stuck with the 260Z carbies. They worked together fine, I think it was a direct swap with no problems (definitely no insurmountable problems). In fact the owner didn't even know it was a different engine, he thought it was identical to what was previously in there!
Since then I have put 240Z carbies on it. There were some modifications to the linkages.. but I got someone who knew what they were doing to do it.