I pour lead into the bottom of an emty clean tin can. About an inch deep, maybe a little less.
Coffee can dia works good for me.
When cooled, peel the tin can way and there's your bench block.
I drill a couple of holes into it, some thru it.
The bottom side will be smoother than the top as it will have been 'cast' against the bottom of the can. But both are usefull.
It never bounces around when driving pins out!
It conforms to odd part shapes easily when needed which I find helpful when polishing on them.
I often open the vise jaws wide enough so the lead block is supported by them. Then place the block on top and work right on it there.
Up high is easier to see (for me) and the heavy lead block doesn't bounce around nor mar any part finish.
Usefull for a weight when gluing stuff together on some projects.
After a time when the surface is beat up enough and un-even to suit you,,re-melt the lead and pour another.
I haven't found the need to do that with the 3 or 4 I have around on the various benches in quite a while though.
They are looking pretty sad of late, but they still do what they need to do.