speaking of this - I once have also done a similar act. It was not a stove though, I got myself some burning red coals and put them in a trough - slipped it under the engine and let it warm the sump with radiant heat.
Started easily after that.
I think fire is a bit too risky considering if the engine had an oil leak.
This was in Pakistan and the stupid hilux was filled with SAE 40 engine oil. I also had to drain the radiator of its "pure water coolant" and fill it up the next day with warm water. - All in all I hated that truck and billed all the work I did as "man hours" to the company