I posted my question over on electronics.stackexchange.com and somebody with some serious chops in analog circuit analysis completely analyzed the currents through the whole circuit, including using the actual gain and power handling specs on the transistors I chose. I won't go into all that here.
But suffice it to say, those resistors are there to:
1. Make sure the transistors turn on because they have a conductive path through their emitters to ground
and
2. Make sure that the amount of current drawn through said resistors is not significant enough to starve the bases of the following transistors in the chain of current.
And he agreed with me that the original values of 330k, 470 and 56 were unnecessarily low, and would only cause unneeded heat dissipation in the transistors. (which is why I bumped them up to 820k, 2.2k, and 220 ohm). He pointed out that the 56 would make sure you could get plenty of current from Q2, so that you could be sure it was turned on enough to deliver 100 mA to the base of Q3. But within the confines of this circuit, Q3 doesn't need nearly that much to fully deliver to the track. If anything, a 56 there was sapping too much from Q2, and raising it to a 220 gets MORE power out of Q3, not less.
But remember, that circuit is from the 1970s, when people didn't worry as much about an extra couple of watts being burned up as heat, and Thorne was probably more concerned with a conservative selection of parts that would work no matter what transistors a hobbyist had in his junk box to build it with. All the resistors in Thorne's circuit were specified as 1/2 watt, just "because". There is no need for that. They can easily be 1/4w, higher valued resistors, which results in less wasted power and a bit more top-end output voltage at full speed.
I made tweaks like that throughout this circuit to get rid of a lot of the wasted power/heat you usually see in a linear amplifier.
