I have two generator welders. One is a Ranger, and the other is an SA 200. I've had others growing up and in business that I've dealt with. But honestly, unless it is a really dedicated, hard core machine and need that you have for such, that sort of thing is so 1990's.
Today, you are better off, buying a good, clean powered generator and buying an inverter to run off of it. I talk to pros all the time who have either done this, or are contemplating this. This way, you can always have what you need and aren't paying ridiculous prices for "add ons" to make your generator welder suitable for the process you desire.
Well, while that may not be a popular notion with some people, it is one that is gaining popularity.
You can buy a 13kw CLEAN power (essentially exactly the same as wall power, if not better) for well less than 2k under the PowerHorse line from Northern Tool. A 9kw is well less than 1k. A competent welder that can carry 200 amps stick/DC tig is 400.00 from us. So for about 2k, you can have a large generator and competent stick welder and you are set. If you want to add other units, like a TIG, which will work on that unit with power to spare and output 250 amps, you can as you need. If you just need MIG, add it for about a grand for a highly competent and portable rig. This way, you can put the unit near you and don't need to walk back to change gears.
Not to mention, the generators have wheel kits and can be wheeled around and are much more efficient than most welder generators. (and in many cases much quieter and easier to maintain).
Honestly, I do love engine drives, especially the growl of the SA200, but inverters and modern technology are slowly but surely moving these units out of the way and into museums. I don't think engine drives will ever be completely replaced, but unless you are needing over 400 amps, I wouldn't even consider it...new or used if I had to do it over again.