Anvil #5 will be the largest anvil I have attempted. Total weight so far is around 700 lbs.
This design is called a "Bridge" anvil, and comes from railroad yard around 1900. The railroads had these made up to 1800 lbs.
I got the design from Richard Postman's Book, "Anvils in America". The ultimate reference work on the subject.
I decided that a simple hardy hole was insufficient for my needs, so I designed a stake-plate of sorts to accommodate a variety of taper sizes combined with a vast array of pritchel holes for punching and such.