Semi rims are large diameter, so you can't get right up next to the anvil easily with one as a base. 

How heavy is that anvil that you are mounting onto the plate? Are you sure of the height that you want it? You may want to do an easily adjusted wood base first to find what height works best for you, and the type of work you will be doing.

My 260# Fisher is just sitting on a stump, gravity alone is holding it.

Biggundoctor just asked the important question. The best way depends upon weight and shape of the anvil. My 250 pound anvil sits on a traditional tree stump and has no other fastening than that it sits in a mitered 1/4" depression to stop it from wandering. Now this is a North Swedish design and that is less noisy by far than the London pattern, which is designed more or less as a gigant tuning fork. My small 70 pound anvil also sits on a tree stump but I have put four 4" nails around the feet. They are only halfway down and bent over the feet. That one is London pattern and tying the feet to the stump this way damped the ring considerably. It is important that the feet have a solid contact at the end if one wants to dampen the noise. (That ties down one tine of the tuning fork and taps the vibration energy down into the stand.) I make the bearing surface of the stump very slightly concave 1/16" or thereabouts.     

5 hours ago, gote said:

... it sits in a mitered 1/4" depression....

Sorry to be pedantic, but I think you mean "mortised", not "mitered".

I probably mean routered since I used a router. However, what do I know I am just a B--y foreigner

On 2/8/2017 at 3:49 AM, Latticino said:

@John, wish we had a like button for that comment.  Going to have to remember that one

Yes that was a good one Cheers

1 hour ago, gote said:

I probably mean routered since I used a router. However, what do I know I am just a B--y foreigner

A mortise is a slot or recess, usually with flat sides. In joinery, a mortise usually receives a matching tenon. If the  joint goes all the way through the workpiece, it is a "through mortise"; if only part way, a "blind mortise".

Since the English language doesn't have a generic word for "something cut with a router"  but instead uses "routed" as an adjective to describe the specific thing so cut, it sounds from your description like your anvil sits in a "routed recess".  However, given that that recess is designed to join together your anvil and its base, it is appropriate to call it a mortise or to say that your anvil is "mortised into" the stump. 

Just to be clear: this isn't meant as personal criticism. I'm just trying to make sure that we're all on the same page, so far as vocabulary is concerned.  English is tricky enough, even before we get into the obscure terminology of specialized crafts. 

I am in no way offended. I forgot to put in a . Mortise belongs to my passive vocabulary i.e. words that I understand when I see it but sometimes do not remember when I need to use it. I very rarely use a dictionary when writing English or German so I sometimes get it wrong. However I think that I wrote routed in the thread 'Show me your anvil'.

I like that definition of "passive vocabulary"; I'll have to remember that.