Unless that 454's been worked over some time in the last 30 years, you're not going to be going very fast towing 12,000lbs unless everywhere you plan on going is dead flat.
Being able to keep up with traffic to some degree is important these days. The roads are a lot different now than in the '70s and '80s. Back then you could slog along at 35MPH and get from point A to point B without hundreds of crazies texting away on their smartphones swinging into the oncoming lane on a blind double-yellow to get around you, or simply plowing into the back of you because they "didn't see."
