R2 thru R8 are candidates for improvements, if Vishay/Dale mil-spec isn't good enough for you.
Also, C3 is the only cap in the signal path, and thus the universal agreement that the $90 per pair Mundorf silver-oil PIOs are well worth using.
For those of you that (claim) you can't read a schematic, R2 & R5 are grid resistors, for a small improvement I'd recommend Takman carbon films.
R3 & R7 are strictly cathode resistors, and not considered in the signal path, although they supply current thru all the tubes.
R4 & R6 are both cathode and plate resistors in the cascode configuration, and likely to make the most difference, I'd recommend PRP or better in those positions.
Caddock MK132 resistors run about $5 each, and I can recommend their use in low level MC phono circuits.
Kiwame resistors are HUGE 2w carbon film resistors that Japanese audiophiles like that cost around $1 each.
Personally I think carbon films have a little more 'grit' in their sound than metal films.
Rikens are another well known Japanese resistor (also carbon film) that run about $4 each.
Shinkon resistors are another well known Japanese audiophile resistor, these are tantalum film, usually considered the best type for true hi-fi, around $4 each.
Tepro is a newer brand I'm not famiilar with, a metal film resistor that looks very similar to the PRP resistors. Tepro is about $1.50 each,
my personal choice from all of these is the 40c each PRP resistors (they are solid red, and were supplied with most of the PH15 phono preamps),
or the Takman metal film type (REY line) which are very good for about $1 each, recommended.