I used to do a bit of being a roadie for local bands in my hometown. Those old Fender amps were heavy!
i have a 1978 Silver Face Twin. Got news for you...those amps are getting heavier as we get older. The JBL speakers will kill you if you drop one on your foot. The coils on those things are impressive.
i have to change preamp tubes and the filter caps (after 40 years they're more than ready to be replaced), but i'm looking forward to cranking it up again as soon as my updates are finished.
Using that amp with my Telecaster will make your ears bleed. When you hit a "Pinch Harmonic" it feels like an ice pick is being driven through your ears, LOL.
The only real problem with the Twins (Pre or post CBS) is that it doesn't distort easily. Those JBL's will take everything you got and beg for more.