tested with:

```
func TestMaxAminoOverheadForBlock(t *testing.T) {

        maxChainID := ""
        for i := 0; i < MaxChainIDLen; i++ {
                maxChainID += "𠜎"
        }

        h := Header{
                ChainID:            maxChainID,
                Height:             10,
                Time:               time.Now().UTC(),
                NumTxs:             100,
                TotalTxs:           200,
                LastBlockID:        makeBlockID(make([]byte, 20), 300, make([]byte, 20)),
                LastCommitHash:     tmhash.Sum([]byte("last_commit_hash")),
                DataHash:           tmhash.Sum([]byte("data_hash")),
                ValidatorsHash:     tmhash.Sum([]byte("validators_hash")),
                NextValidatorsHash: tmhash.Sum([]byte("next_validators_hash")),
                ConsensusHash:      tmhash.Sum([]byte("consensus_hash")),
                AppHash:            tmhash.Sum([]byte("app_hash")),
                LastResultsHash:    tmhash.Sum([]byte("last_results_hash")),
                EvidenceHash:       tmhash.Sum([]byte("evidence_hash")),
                ProposerAddress:    tmhash.Sum([]byte("proposer_address")),
        }
        b := Block{
                Header:     h,
                Data:       Data{Txs: makeTxs(10000, 100)},
                Evidence:   EvidenceData{},
                LastCommit: &Commit{},
        }

        bz, err := cdc.MarshalBinary(b)
        require.NoError(t, err)

        assert.Equal(t, MaxHeaderBytes+MaxAminoOverheadForBlock-2, len(bz)-1000000-20000-1)
}
```

by using math.MaxInt64

See #2184 (comment)