[Collins] Need advise on diode load tube amp AC/DC

[C E]

All:
I recently picked up a salvaged AC/DC type tube audio amplifier from an RCA record player. I intend to use it as a diode load amp for my R-390A and 51J-4. 
 
 I have two concerns: 1) can I get away with physically isolating the amplifier from the chassis without an isolation transformer while preventing any AC voltage leakage when interconnecting the radio and amp together?  2) I suspect the input to the amplfier was using a magnetic phono cartridge.  Will this be an unsuitable impedence input to the amp when tapping signals from the diode load output. Thanks. 
 
Cal, n6KYR/4