[Arran]

With regard to this being a "Hot" chassis, point in fact it is not exactly true though you still have to use caution. Philco preferred to isolate the B- or power line from the chassis by running an independent bus, then they would couple the steel of the chassis to the B-with a large paper capacitor like .22 mf and a 220,000 resistor for shielding purposes. In sets like these Philco would often use a strange choke and capacitor assembly instead of a straight capacitor in this role, I think that the idea may have been to block interference of some sort at the time, maybe from low frequency marine beacons.
I've been working on AC/DC sets for years and I never bothered using an isolation transformer, just common sense. It's actually fairly simple, keep the set unplugged except for testing, when you are testing keep one hand behind your back. It can get tricky while testing for voltages sometimes but the probes on the volt meter are insulated.
Regards
Arran