d30 center sections are ductile iron, while d60 centers are nodular. apparently nodular is about the easiest to weld, while I guess ductile isnt that bad either as far as welding to cast iron goes. From searching around over some time now, I am slowly deciding that I will probably just tube around/over the center section and not to it if possible

 

i wouldnt... you can also adapt it to the top bolts for the cover and get longer bolts... seen that done a lot as well...