I think it should work -but I'm no expert. Just in case it doesn't, keep a copy of RSD Lite and a SBF of 2.2 -just in case.
Make sure that your stock rom is, well, stock (cityid, kindle, amzn, etc). The cleanest way according to the experts is SBFing.
After the OTA you will (may??) loose root so make sure you have z4root handy on your card as well as the bootstrapper.
I think your idea should work -maybe more experienced users can confirm. I was going to do exactly that but my stock rom backup did not have cityID, so I went the hard way (it took an extra 15-20mins but it is the cleanest way)
Good luck. Post if you have questions -there are a lot of people that know their stuff here and they're willing to help.