Bruce,
Some of your questions might be answered
in this installation guide. There are a few differences between a 53 Air Flow heater installation and earlier heaters.
I have an in-line fuse (in a 54 that is similar to yours) between the fan control switch and the heater (I do not know what size fuse). The location for the copper line is shown in the manual.
I think that Denny Graham has some good photos and instructions - he'll post them, when he reads your question.
