You can accomplish what you want with what you have, or similar to, but it takes a lot of time, learning and patience.
As stated previously, be on the lookout for a 261. I've had my ears open for a couple of years and come up empty, but I live in a relatively small area. A 235 would do it too, although with a little less torque due to shorter stroke.
Get a T-5 behind it if you're not using it for heavy work, or if you are using it for work go with a SM420 or SM465 with a Gear Vendors overdrive or a Ranger overdrive.
Gear the rearend so that your're cruising about 1500-1800 rpm at your chosen freeway speed. There are many calculators available online. Remember to include your overdrive percentage.
That's all the easy stuff, mostly bolt-in. All of it commonly available.
Next is to super-tune the engine. That doesn't have to mean build a racer. The purpose is to get the fuel and timing curves where they need to be. Even a simple 1 barrel carb like a Rochester B can become somewhat complicated until you learn all its circuits and total operation. I've found B's to run very rich as delivered. This can be addressed, and fuel economy greatly improved, but there is always a tradeoff when working with a carb. As a mechanical device it is functional, but certainly not ideal. Being as how it operates off of vacuum, the more vacuum it sees, the more fuel it feeds. At the point where it needs the most fuel, it has least vacuum, and has to supply enough at that point. By that nature, they tend to feed too much fuel the rest of the time.
Electronic fuel injection, on the other hand, when functioning properly, supplies fuel based on vacuum, temperature, ignition timing, and throttle position for much more precise metering. It may not look like an original carb, (this is the HiPo shop, right?) but works infinitely more precisely.
That said, I'm pulling avg 20 mpg out of my 55 2nd 3100, 235, SM420 and 3.55 gears with 30" tall tires. I'd like a Ranger overdrive unit, but can't pull the funds at this time. I cruise down the highway at 2400 rpm, just about the top of my torque band, at about 63 mph. There isn't an orifice in my carb that hasn't been massaged. I'm also willing to accept (for now) that under very heavy load it is too lean. These carbs don't have a power valve, so whatever it is jetted at is how much fuel it gets.
There was a build on here about a year ago by drummin52, putting fuel injection on a 235. He did it all with junkyard parts if I remember right.
In the end, if you stay with a 6, you'll generally have an original look, but never a great power house. If you want gobs of torque, stick a Duramax in it.
Devin
