I'd check/clean input jack ground first. Make sure they are tight to the chassis. Make sure the star washers are present. Check that all of them have hot grounded when no jack is installed. If not, give them a clean with contact cleaner and then by slipping some rough paper between the contacts...
I wouldn't risk it. You might get lucky the first 20 times, but the odds of doing damage are there every single time you flip. Probably not a big risk, but a risk is a risk.
All electrolytic caps should be replaced -- as stated before, it may be quite a bit less expensive to use appropriate value single caps (mounted securely) in place of multi cap cans. Clean all pots and jacks. Check bias. Then evaluate what's what before doing anything else.
My R8 is an amazing instrument, worth every penny. It gives me great pleasure. That said, when I want to gig a Les Paul, I usually take out my $550 Indonesian PRS.
The amps with no screen resistors still have the screens connected to B+. Your broken resistors did not pass DC, so no voltage on screens. Amp should made sound, but low volume and distorted without screens.
Did you mechanic do a scan to see any stored errors? An '08 means pretty much everything goes through the ECU, and errors should be triggered and stored until cleared.
That Reverb transformer is being driven with about 1-1/2 to 2 watts of power, as opposed to an output transformer's 15-100 watts, so I wouldn't worry. I have seen amps run without a reverb tank for many years still be fine when one is hooked up.
I don't like the heater wires running under the jumpers on the tube sockets. They are a source of noise, and run a fair amount of current. If you do Marshall-type heater wiring down at the chassis, you need to run around the outside of the sockets. If you do Fender-style flying heaters, you want...
I like to have an old tube in the socket when soldering to prevent solder from running down the pin hole and as a bit of a heat sink, keeping the heat where I want it.