I think you're going to find that the Super Hornet 300 is the same as the Miller Big 40. Even though Airco labeled it as a 300A unit, it should top out around 400A. I owned one for a short while earlier this year, long enough to get it running and trade it straight across for an XMT 304. You'll have to go through Miller's manuals for the Big 40 and i.d. this one by looking at the faceplates on the different ones until you match the gauge and receptacle locations, and control knob style to the exact Big 40 year range. The 110V current is probably going to max around 3KW so you aren't looking at a powerful generator. But at least it's AC current. The engine is going to be a Continental F163 with a top-mounted distributor vs magneto like the SA-200's use.
I can tell you that even though it's a rectified AC machine, it can still lose its field magnetism just like an old DC welder can - so unless you have good reason to know the armature is bad, it could just be that the fields need to be flashed. I had to flash the fields on the one I had three times before they'd retain polarity between shutdowns, don't know why. The weld quality was OK (nothing to write home about), but the arc had a distinct buzz to it that I haven't heard on an engine drive before. The machine is probably best used for something needing lots of amps and not a lot of precision - if I would've kept the one I had, I'd have used it for a gouging power source.
As far as value, it's worth a couple hundred bucks if the armature is bad, and it's a parts machine at that. The F163 will be valuable to the Lincoln guys. The machine won't be worth putting the money into to fix. If it just needs flashing, then IMO $800 is an OK but not screaming good deal, *if* it will do what you need it to. It'll be a fuel hog by comparison to modern air-cooled or diesel welders.
