I've personally done my bike (not an XS, but an old honda I built last year). A local shop allows people to come in a "rent" their vapor blast cabinet on site... it's definitely a process...but boy does it work. It's a glass bead slurry with high pressure warm water. Works like magic and literally removes everything and makes it look like new. It easily removed the yellowed clear-coat, baked on grime, stains, bits of gasket that wouldn't come off, etc...
Other than it's very time intensive, and it needs to be cleaned thoroughly afterwards, I wouldn't think twice about doing it...Note: I've only done it on a fully disassembled engine...case halves, side covers, head, etc. (Which allowed me the time to take things apart and do it in "batches").
I don't think it would be a big deal to do it to a complete engine but caution that if any bit of the slurry gets past the intake/exhaust/breather holes, etc...it would require a total tear down, simply because that stuff needs to be cleaned out and you don't want it in your engine...I'd probably make some cover plates for every access point so you know for sure there's not a chance it can get in there.
Good luck!
