What is the best rod to use when welding cast steel (specs unknown) with A36 structural angle? The weld will not be considered strucutural.

You need to find out the carbon and alloy content of the casting. Until you have that information, discussion of a welding procedure is premature.

What is the welding process? If not structural, what is it considered?

Tack welding the structural angles to machine base to prevent possible movement.

Tack braze welding by oxyacetylene flame using a bronze rod and suitable flux may do the job without melting any of the base metals.

http://www.welding-advisers.com/

The cast material is a ductile iron 80-55-06. This is approximate as the material I was given is a Europeon standardard (EN-JS 1050).

To tack weld 80-55-06 ductile iron to steel, use Ni-Rod 55 stick electrodes.

Any preheat of the iron required before welding? Thanks for the information.

According to one manufacturers spec this material contains ~ 3.5 C so you should consider preheating and slow cooling. Id suggest around 400F for preheat.

I have seen various manufacturer's literature on these nickel electrodes stating that pre-heat is beneficial, but usually not necessary. It does no harm. I have never seen a recommendation for slow cooling.

I would suggest you review the information below for welding ductilr iron:

http://www.ductile.org/didata/Section8/8intro.htm

If I could count the ways to successfully weld the irons to Carbon Steel.
The information posted by [b[metengr[/b] is very good and should be used if possible.
In our old textile manufacturing plant we had to weld all the irons to CS. We welded Ductile, Malleable. Meehinite, and many others, some for the thirties.
The only absolute way to weld the Irons to CS would be to heat the materials to above 1325°F and weld at temperature. As this is normally impractical, an alternate approach is to weld “cold”, in other words get the heat input down by “painting” the metal instead of welding. This is possible due the filler being so much stronger than the base iron. This process takes a little getting use to by a good welder because it profanes all he has learned about welding. The success rate is very high even on some of the older oil soaked irons. On very dirty iron we will try to run them through the Pyrolysis Furnace to achieve the cleanest surface possible.

We use a Chronotron electrode 210 or a Certaium 889