Just recently finished a similar project for a similar purpose. A couple of things I've noticed. Unless the lags holding the anvil down use lock washers, all the pounding will cause the lags to back out. I took mine out, installed lock washers, seems to be holding. I have mine on a piece of 8x8. Unless my work piece is well centered, the anvil really tends to jump and bounce when I smack it. Haven't solved that problem yet.
Make a takedown bow from skis!