The DC offset is a function of the bias adjustments. Unlike later designs, there is a separate bias adjustment for the upper and lower transistors. This could be caused by your 17 mV bias if the other transistor is 26 mV. If you make adjustments, be careful because an intermittent open on one of the pots will cause problems.
There is a better way to wire the buck transformer. Connect the upper AC line to the upper end of the secondary and connect the upper end of the 110 V output to the top of the primary. The primary to secondary jumper will then be from the top of the primary to the bottom of the secondary. The input sees both windings in series with the output across only the primary.
If the bias has been changed to a non adjustable circuit, then you are subject to component tolerances. I had one that was good on one channel but quite a bit off on the other. That's when my bias modification was designed to return to an adjustable circuit. If the bias modification is similar to what they did for the 600-T, you might try adding a parallel resistor to slightly change the resistance value in the bias string. As an example, a 3300 Ω resistor added in parallel with a 270 Ω will bring the total down to 250 Ω. Since I don't have the exact schematic or the specifics of where the problem is, you would need to determine which resistor might need the change.
Do your transistors have a color dot on the flange? This indicates the beta group. They should be the same color or at least each pair the same color.
The transformer wiring is shown and explained at the following link. It is about halfway down the page.
http://sound.whsites.net/articles/buck-xfmr.htm
Concur on the diode part number. 1N3754 was also used by RCA in similar applications. This circuit is basically a design from an early 60s RCA manual. However, on the 600-T, the diodes were nowhere near the heat sinks, so they could only compensate for ambient temperature. Before purchasing diodes, you could also swap them and see if the problem follows a diode. Use an alligator clip on the leads as a heat sink while soldering as these are germanium. Get the iron hot and get on and off as quickly as possible.