I understand that welding cast metal is becoming a lost art, that being so, I am looking for any helpful tips on the subject. Depending on the cast type, I am told that I should use a high percentage nickel rod(Nirod?). Also, what Pre and post heating procedures should I follow?  Any tips would be greatly appreciated.

As a former alloy salesman, you need to know what type of cast you are welding .Usually a spark test might tell you if it is grey ,mallable or ductile. A high nickle rod is best  and try to keep the temp UNDER 500 degrees.Drill stop any cracks and prepare with a deep bevel .Skip weld to tack . and watch your color.Nickle rods are very soft and flow very well so a lower temp is ok .(Remember UNDER 500) So take your time and allow it to cool down. For post weld you might need to "peen" your weld to relieve stess.DONT put your weldment under sand or a blanket or anything that might harbor moisture.
Also dont be afraid to spend higher dollars on a good alloy,The higher the nickle the better the end result will be . GOOD  LUCK !