You may have the normal "bad internet info" thing going on.
The master volume Twins (and other Fenders) can easily sound as good, or better, than a blackface. The master can be removed VERY EASILY if one had some kind of thing about it. It would be better to replace it with the Torres Dual Stage Master for much better tone.
These amps can be "backdated" with our kits very easily and thousands of musicians world wide are getting the tone easily from these amps.
In general, the 100 watt models are so close to the blackfaces the changes are quite easy.
(Part# (Pre CBS) Pre CBS Kit for Fenders $17.95
The most famous kit. A conversion for Fender amps made before 1980 to "Blackface specifications" plus aged circuit technology. The best sounding conversion. Very easy to install.)
An overview of the technology is in "Inside Tube Amps"
We grab as many silverface Fender Twins, Pros, Super Reverbs, Viborluxes as we can find as we ALWAYS get the sound from them - absolutely no problem.
The 135 watt Twin (and 70 watt Pro and Super Reverb) have one Chararastic that is different from other amps - they have ultra linear output transformers giving them more power and wider frequency response.
The poorly educated techs and those with no knowledge instantly reject these amps as they are "different." I, personally, seek them out as they can certainly sound the absolute best for clean tone - there is nothing like Ultra linear operation to get a big, full, clean tone.
But, since the amps do not have adjustable bias controls, and do have circuit changes (easily reversed) they are rejected without taking a look at their great technology and incredible quality (far, far better than any other amps of the era.)
These things are easily fixed.
Bias Notes $5.00
Instructions for setting the bias on common Fender and Marshall amps. Includes the rewiring necessary for non-adjustable bias Fender amps.)
If you really want to get all the details right check out:
A kit to rebuild the Driver section of Fender amps with two or four power tubes (except the Princeton series) Includes design and parts for several versions of Pre CBS drivers.)
the 70 watt models (pro, super reverb) do not have rectifier tubes and are therefore further rejected (easily fixed)
we have a kit to add a 5U4 rectifier tube to any tube amp. Includes instructions and all parts, can be done on amps without proper power transformer.)