There is a lot of info - mostly summaries of historic allowable stresses/designs. You will find that allowable stresses got lower and lower with cast iron eventually being eliminated as a building material. Try Friedman's book historic building construction, a summary in the back covers the progression. Google will also give you lots of good info.
Don't try to weld or modify them. Also keep in mind that all connections are basically pinned at each floor level as each column stacks. If you are removing floors the bracing is tricky - usually collars being careful to not clamp down too much.
Very brittle - I have seen very thick base plates snapped in half.
One thing that gets overlooked often - even if you don't increase loading you can still cause problems if you change loading path such that it creates an unbalanced condition, i.e. moment which causes tension on one face.
See attached for one paper.
