Myself, I would get either a 250 or 292 to build. The 292 has a longer stroke and taller deck. But they are also a little harder to find parts for, especially brackets for AC and PS. The advantage of the 250 is there were many more made and they will drop right in where the 230 is.
The 230 was a decent engine, but will take more work to make it like a 250. I look at it as starting with something better and having a running truck while you're working.
Another site is
www.stoveboltengineco.com . And an excellent book on building these engines is Chevrolet Inline Six-Cylinder Power Manual by Leo Santucci, available thru the on-line stores and
www.inliners.org