Hi Andrew,
Don't let the newness get to you. if your truck is rated at 9,200lbs your truck will pull the trailer. The wrong gear ratio in the truck might make you a bit slower on the big hills, but other than that the truck will pull the trailer. People have been pulling similar weight trailers for many years with vehicles that have significantly less horsepower and torque.
Can you give us the year and model of the truck? Is it 2 wheel drive, 4 wheel drive? Long bed, short bed, crew cab, standard cab? Did the dealer tell you the axle ratio, or just that it's the wrong ratio?
Yes tongue weight is important, and we don't like to guess because we don't want you to have to spend additional money to correct a bad guess. But I'm going to "guess" that a 1,000lb hitch will be fine, and definitely not more than a 1,200 lb hitch.
In reality we're talking 200lbs difference and you're probably going to get more than that fluctuation in just camping and using the trailer for a weekend. When I camp in the desert I easily add 200lbs to my tongue weight for the trip out. After the weekend my coolers are empty, the fresh water tank (in front of the axles) is empty, and the black and gray tanks behind the axles are full. And I get home towing 55mph without any sway.
Yes it would be nice if you could take the trailer to the scales and get a tongue weight. If you can't do that though, then here's what I would do.
Send your wife to the store to buy you some more beer because you're getting low. While she's gone run into the bathroom and grab the bathroom scale. Then follow this link to get your tongue weight.
Bathroom Scale tongue weight Make sure you use method B :)
Or another thing you can do which is not as precise but probably just as good. You have bought a standard run of the mill 28 foot trailer. Call Progress MFG (the makers of the Equal-i-zer)1-800-478-5578 and ask them which weight rating hitch they sell the most of. I'm guessing that they tell you it's the 1,000 lb model. If it is the 1,000 model then that's probably the model I would buy.
You also asked about the different hitches fitting. The hitches are all basically the same size unless you get up to a class V hitch which is not a stock hitch on your truck. The different weight class on the WDH is the spring bars. (the bars between the hitch and trailer A frame) They will all fit your trailer, but you probably can't buy a 1,000 lb hitch and later put the 1,200 lb bars in it. But I guarantee you that if you call Progress they can tell you for certain if upgrading to larger bars later is an option. :)
One more thing. Go out to your truck and look at the hitch. Is there a sticker on the hitch that tells you the capacity of the hitch? If so what are those numbers?