Keep in mind that really are only protecting the power feeds to the fuse block and ammeter. Most all of the branch circuits are fuse protected (with MUCH smaller trip limits than what you are contemplating) and will blow long before your breaker or beefy fusible link. You are talking about adding additional connections (a source of problems/shorts) in a relatively short distance of a circuit (dash to alt). I would think your concern would be better spent making sure your alt to fuse block power feeds are in top-notch shape and routed in manner to avoid trouble (abrasion or heat). Make sure connections are clean and tight--including the ammeter!