You don't need lime necessarily, you just need to keep the heat in the part as long as possible. Sand, Weld blankets, something that doesn't conduct heat will do.
I would Preheat in the 150-200 degree range and that should be fine. Stick it in the oven to do that, don't hit it with the oxy.
As Cast Iron cools, the microstructure of the metal changes. Crudely put, the faster it cools, the less desirable the changes are, so you want to slow the cooling down. Hence, preheating and then insulating it after the welds are laid should give you good results.