, the big hammer head is a pretty common anvil for small work, both in Indonesia and in western countries. Just about anything that is big enough for the intended work can serve as an anvil. My first anvil was a section of railway track, I've taught a few people and they used sledge hammer heads, railway track, pieces of machinery as anvils. The trick is to mount the anvil on a good solid stump and sink that stump deep into the ground, somewhere between half a meter and a meter. The difference between a big anvil and a small anvil (like a bit of rail track or a hammer head) is that a big anvil makes the job faster and easier. I learnt on a 150 year old English anvil that weighed 350 pounds, it was really easy to work on. My own anvil is only 75kg (165pounds) and not as fast nor as easy.
This has probably been seen by a few of you, but it might be of interest to those who have not seen it:-