anyone out there know if anyone makes/ or if there are any swaps for a chevy 250 for a high output (140 amps) alternator?

If it fits a V shaped Chevy engine or any other GM passenger car / light truck it will fit on a 250. The aftermarket 140 amp jobs that use the Delco case are a physical exact replacement. If you are running an ammeter the range needs to be enough to indicate all the amps that passes through it. A voltmeter doesn't care as it only displays the voltage output. To get the full benefit of that alternator's amp output you need to run at least an 8 gauge wire from the Batt terminal of the alt to the battery. Wire is like pipe, the smaller it is the less volume that can pass through it and amperage is the volume in an electrical circuit. Amperage does the work, voltage only gets it there.

Mike

thanks very much for the info. i already have the wires upgraded due to my involvement in the car audio scene...all i nned now is a decent alternator.

Look into a Powermaster alternator avail from any on line or local speed shop. The one wire jobs can be also wired as a conventional 3 wire and that eliminates having to rev the engine to get it started charging when the engine is first fired up. A minor thing but a lot of people find it more convenient to have it charging right off the bat at idle. As far as neatness of the wiring re: one wire versus the 3 wire set up, some people can still make a mess out of just running a single wire so it really is not a big deal on a car that is a driver if you work neatly.

Happy to be of some help,
Mike