When I ordered parts for this I had to settle on a 25k trimpot instead of the 20kB the pdf calls for. I didn't find the 20kB at Mouser, ppp, or smallbear.
Will I be ok w/ the 25k here?
Yep. No problem subbing that. Also, it really means 20k, not 20kB. Most trimpots are linear (maybe there are some audio but I've never seen one used).