If I didn't have an anvil I reckon this block would do the job.

We dragged it out of the scrap pile and no -one seems to know what it is. It now rests in my forge area and is an exceptionally good upsetting block. 

Someone suggested it might have been the bottom part of a hammer, the slots holding the bottom dies maybe. Those slots are handy benders. Someone else reckoned it could be a tractor weight, but you'd need a forklift to put it on.

I guessed the weight at around 300 lb but the way it made the Dingo buck it could be more. A quick calculation (disregarding the slots) works out at nearly 550 lb but that seems a bit much. Bottom block is 350 x 370 x 140 and the top part is 230 x 170 x 370.

Anyone know what it may be, and could it have a better use than an upsetting block??

 

Have you done a spark test to see if it's cast iron or cast steel?

Those cut outs seem a bit oddly placed for a power hammer's anvil or sow block.  It could definitely be repurposed as such and I'd highly recommend it if you do decide to build a power hammer.

Just a first glance makes me think of the counterweights used on big cranes.  

the only thing about a crane weight is the fact there is no way to pick it by the crane.  but i also think some sort of counter weight.  

you could use it as an anvil.  it does have the mass and if you are hitting hot metal will work well.  you have unlimited attachment options with the slots.  will be a fun piece to play with.