I cost me far more to move my big hammer than it did to purchase it
And these hammers require a large hole with some fairly complex form work.
Did it have a size marked on it?
Anything over 200 pounds requires some serious CFM.
Had my vise bolted to the wall of the shop, and of course I broke that loose. Gathered up some drops/jacks/tractor parts I had laying around the shop and made up a quick and dirty stand. Shop floor is dirt so i cast it into a block for stability. Did a "tap root" in the bottom of the hole about 36" deep to help resist any twisting forces. So far so good, very solid. Only cost me about $20 in concrete.
Its a spare lower die for my big hammer, its designed to put a single sided taper on spud bars. Weighs about 300 pounds.
The plate under its 1" thick, not any flex that I can detect, when you forge on it feels pretty solid.
Took a short video of my hammer after I have done some work on it. When I set it up it would only do no blows or full blows. After lots of fiddling with I'm pretty happy with the control now. I was working on a kukri style chopper I forged down from a brush cuter blade. Using a flatter I made to adjust the profile a bit.
Pour an inertia block. I have my hammer bolted down on a dirt floor shop. I left the form boards on it to protect the edges. It will also help with an under weight anvil.
I would use that steel in the hammer frame and not a large base. The hammer will need to be bolted down anyways. I know little giants have hollow anvils, my 50 pound did, and i have heard other brands do to. Obviously a solid anvil is best but LG's have moved lots of metal with hollow ones.