The SA-200 is a super durable machine. Aside from running it out of oil or water, you really can't beat them. The model states a 200 amp but it actually peaks at about 300 amps. You can gouge off of it and TIG and stick and wire and , ... you name it. The weight of the 200 is a bit over 1200 lbs. so you might want to consider this when you decide to upgrade. It weighs  twice the weight of your ranger -soaking wet. The longivity is unsurpassed also. As you noticed there are machines still out there working that are from the 40's and 50's. I had a 1946 model give to me . I couldn't get it to run , so I sold it to a buddy . He had it running in 30 mins. Running and burning rod. I wish I had it back, but he won't sell it back to me. The 200 also isn't your normal welder/generator . It only puts out 3000 watts and it is only D/C. No A/C power could be costly due to upgrading your tools to A/C-D/C tools. An A/C drill lasts about 5-10 mins. then it goes up in smoke. Just thought I would throw out some of the things I have learned since owning a 200.

Along with what Pyplynr said, I have found the Lincoln machines to just run a smoother weld.  Especially machines like the SA-200, SAE-300, and others.  My OLD SAE-300 would run so smooth it made all machines I have had since look sick.  Has to do with engine rpm, generated frequency of the arc, heavy duty generator, and I'm sure many other factors.  I maintain that if a person could not pass a test with one of these they really didn't know how to weld. 

For being a gas drive, the SAE was very efficient.  Diesel was more feasible for a lot of guys because it was so easily available at their job sites.  But gas can always be an alternative now that we see diesel more expensive than gas and the difference seems to be there to stay.

Have a Great DAy,, Brent