needed high amp alternator

By "to be safe", you must mean "insure the battery stays charged" since 200A is a lot of current to play with. What indicates that the current alternator is not doing its job? Is you battery running down so that you need to put it on a charger once a week? The only way to diagnose real-time is to use a clamp-on DC ammeter to measure various currents, but even that is hard since they vary w/ rpm, as fans come on, etc. Don't go by the current ratings on the fans, since that is often just the starting current surge, plus fans don't run all the time. I made some quick measurements on my modern vehicles (fans, fuel injection, ...) and see ~60A max w/ both fans on, so their 120 A alternators appear more than sufficient.