WIth vintage amps they tend to use alot of Carbon Composition resistors. They are noisy buggers
BUT after you change them then you realise the magic of the amp is gone. The Carbon Comp Resistors are very musical and fuller body resistors compared to modern day resistors.
When he changes the amp try to ask him to get new Carbon Comp resistors. The later production of this type of resistors are much better. Worse go for carbon film, not too bad. An example of this is the reissue Mac amps previously everything is made with this CC resistors when they reissue they did not use the same resistors. I did not like the updated Mac though.
Next alot of old amps are made with coupling capacitors, try to ask him to install back the same variant. MOst probably they were made with Polyester film capacitors, this would give a less detail sound but warmer and more body than other variants of capacitors. FOR solidstate amps i think they work great better than most caps i know unless its perhaps the Mundoft Silver/gold series.
Ecaps are like the Philips variants good for Solidstate. And closers to NOS e-cap sound
Boosting power tends to stress the component which is fine but it reflect in the sound. So boost the power but pay attention to sonics
If the guy knows what he is doing in terms of sonics then all means go ahead.
My opinion and other might vary
