Yes, there's a lot of misinformation on the web about these swaps, everything to do with suspension has fairly critical measurements, even choppers, or you just couldn't ride some of them. A longer swingarm may even up the steering, as in slow the rear input as well but once again its a measurement, not just throwing in a modern swingarm, which are usually up to 6 inches longer than stock, far too long for a good handling bike. The 500-550 actually have a longer arm than the 750's which a lot of people don't know, if i were to go longer on the rear i would be looking for something an inch longer or round abouts, There's a guy {Carpy} that makes boxed 750 swingarms in 2 inch over, on a 500-550 they would be about an inch longer. In saying all that, I would leave it as it is for now anyway, build the bike, ride it and see how it feels to you, if you don't ride aggressively at all it may feel ok to you. You shouldn't need to use a steering damper as the longer trail adds stability, so it should not need one. Once again. thats will depend on how the bike feels to you, i use dampers on all my bikes but i still like to ride quite hard now and again and i have used them since the early 80's on every bike i've owned....