Only need to order some caps. I'm thinking auricaps for the output. Don't know what to use for the cathode bypass but being only 16v I guess there's some exotic things possible? Of course Auricaps would also be nice there. And maybe mills 12w for the cathode resistors?
Edit: PE has the mills for 4.25 ea
If you plan to put in the stepped attenuator, I would wait to install any upgrade caps until that's in. It will slightly alter the position of the coupling cap in the left channel if that capacitor is sufficiently large (I think more than 1.25" in diameter).
The cathode bypass caps that come with the kit are pretty exotic, though a higher end line of Nichicon capacitors has been released fairly recently (KA I think?). YMMV on what fits, I spec'd in the manual that the top of the cap should touch the nylon standoff close by. I think a little more diameter would fit, but probably not more length.
The Mills 8 Ohm/12 Watt/1% resistors are a nice choice, and actually a very easy retrofit once the kit is complete.