Welding cast iron is 'tricky' and with the cost an avilability of good headers today, It's just not worth it any more.
"spiting" started in the late 40s because there were no headers then and it was a 'cheap charlie' way to go for the Muffler Shops.
Langdon has a good set I'm told, or you could get a C-40 truck manifold. There are steel ones too.
Good luck.
