Please trust me on this one, I've been knee deep in amps for more than 20 years - DO NOT change the blue molded jupiter caps in the pre amp section unless they are electrically leaky or produce dc on a pot. There is absolutely no truth to "orange drops are better" or other snake oil caps that are spewed about on the internet. Do to RoHS, changes in polyester substrates, cap manufactures being bought and sold etc, caps today will not sound the same, they certainly are not made the same.
Additionally, only change the plate load resistors / signal resistors if there is popping or other artifacts due to the CC resistors - they have drifted over time, ie aged, and replacing with new caps and resistors will change the tone of the amp - in effect, returning the amp to its' infant tone of 50 years ago.
As I said previously, start with replacing the paper electrolytic bias cap and HV filter caps under the dog house - stop there and evaluate before continuing. Look at Hoffman amps for more info / parts, mojo, antique etc. My choice would be Hoffman or antique (tubes and more). Doug (Hoffman) is a damn good guy, and hosts quite an active amp forum.