Hi,
This is an excellent catch, congratulations.
Re: Servicing the FM. If you have serviced an AW in the past there is no reason to be too afraid of the FM. The bearings, dust covers, cones, etc are all the same, as are the driver and clutch components, pawls, springs and RH pawl pins.
Aside from the obvious additional components associated with the addition of the fourth "power path" , the overhaul of the wear components is essentially the same as for the AW.
Someone else mentioned the issue with "tooth" breakage on the LH Ball ring. If you find this you will have to find a parts hub in good condition to salvage the shell/LH Ball Ring.
Probably the most important area to exercise caution is with the two part indicator rod. They are scarce and the LH portion threads into the RH "coupling" (rod) with a small diameter/ extremely fine thread. To add to the fun, the rod threads through a compensating spring c/w a small (but critical) collar and through a clutch key (not too different from the AW). The Sturmey Archer service manuals available from the Hadland Blog are a great help in terms of techniques to install the rod, etc.
One other area to note is that the LH pawl pins are different from the AW. Later ones were riveted (lightly?) in place with a primary planet cage that allowed support of the pins from the back. My 1949 hub has loose pins and a planet cage with no cut-outs to allow access for the "anvil" for riveting the pins. This might complicate renewal of the pawls. In either case, the low speed pawl pins are different than those of the AW and I haven't come across any during online searches so take care not to lose them (although they would be easy for a machinist to duplicate).
The clutch, low speed and compensating springs are a "matched set" apparently and were sold together as a package. Re; rebuilding, it is a question as to how critical this is - SA changed the springs from a a stiffer set initially installed to a "soft" set sometimes in the 1940's so I suspect the warnings relative to the springs was to avoid mixing these two different stiffness springs. It is a bit of a "moot" point as the only springs readily available currently is the Clutch spring and the likelihood of finding a spring set is pretty low.
Compared to the AW, there is more inherent drag in the four speed mechanism. The manual mentions this: "The gear internals are rotated during freewheeling...., therefore, providing cones are properly adjusted, a slight pull on the pedals and possible rotation during freewheeling is in order". I noticed this spinning the unmounted wheel and had observed some very light "polishing" wear on the outboard face of the Gear ring without any obvious marks in the inside of the RH Ball Ring during the servicing.
I would not be too concerned about doing the service. The normal approaches apply; careful disassembly , photos, notes and downloading the service and parts manuals from the Hadland blog should assist.
