ZFT,
All straight pipe (non fan) series B707's had the parallel yaw damper fitted (either yaw damper or autopilot, as you indicated), whereas some (but not all) fan powered (non-advanced) models had the series yaw damper, which remained engaged for all flight regimes.
The B/C advanced models had many improvements.
A larger vertical stabilizer/rudder, improved Q-feel for the rudder power, series (ie: full time) yaw damper, advanced cowl, full span leading edge devices, improved trailing edge/fillet flaps, and most important, more responsive engines (JT3D series), yielding much improved airfield performance.
An altogether different aeroplane.
Did my original training on the B-advanced model, then asked the old-timers at PanAmerican to indicate what I needed to know about the older aircraft, as these are what I would be flying.
They mentioned they were a bear to fly...and they were right.