Fox 38 Rhythm - Is it possible to upgrade damper and change travel?

I don't have the level of knowledge you want on that fork, but from what I recall the Rhythm forks are very similar in construction to the current (Fox owned) Marzocchi branded forks. I know the Zokes use 6000 series aluminum upper tubes, vs. the 7000 on the high end Fox forks, and thus have a higher wall thickness to compensate for the weaker material, so I suspect the Rhythm forks are using that same construction.

Regarding interchangeability of Fox parts, you'll need to get someone with more hands on experience with them than me, but I did just want to throw out there that some aftermarket parts are inter-compatible, so even if you can't get a Grip2 damper, you may be able to get a 3rd party damper. For example, these Avalanche dampers are supposed to work for both Fox Performance and Rhythm forks, although each one is custom made for the user so I'm not sure if the fittings differ for Performance vs. Rhythm but, either way, it is an option:

http://www.avalanchedownhillracing.com/Fox%2040/Fox%2036%20Open%20Bath%20Cartridge%20Kit.htm

BTW, I love your work...big Curb your Enthusiasm fan!

Not sure about 38s specifically but the air shafts between a 36 Rhythm/Marz Z1 are different than for a 36 Performance/Elite/Factory for the ever so slightly different thicknesses, had to navigate that recently to up the travel on my fork. Haven't checked the damper compatibility though!

Yeah, that does sound pretty pretty pretty gooood! I've thought about doing the same thing, either getting a closeout basic fork or a cheap used one, and just using the chassis to experiment with different internals. I go back and forth on it, as, on the one hand, Fox has a huge R&D budget, and exposure to all the pro athletes tuning preferences and the institutional knowledge therein, so you'd hope that after almost 30yrs they'd have their Sh*t dialed. On the other hand, most of the aftermarket tuned forks and shocks I've tried have felt great, and certainly better than stock, so it really seems like there is something the big guys are missing. And I know that there's the explanation/argument that the stock Fox/RS product has to fit the "average customer", plus a reasonable range below and above average, and isn't able to be customized to the end user's needs the way a boutique tuner's parts are. But I still don't fully buy that, because I would say that I, and most of my riding buddies are average in size, and we'd hope a bit above average in ability (but realistically not hugely so compared to Pro riders), and yet these aftermarket tunes still feel substantially better. After a few experiences like that, the idea of getting a cheap chassis and then custom internals from a 3rd party starts to sound like the smart money way to go, as it can actually cost less than going for the premium models from Fox or RS.