The project log is written backwards.  After some initial success, the development will be described.  In short, it worked better than expected.

• A PIC16F18345 EVB is configured to generate 400-500kHz using the NCO peripheral
• Sweep is generated by a for loop and updating the NCO registers
• Internal HF osc is configured for 32 MHz.  Supply is 5V from USB port.
• Frequency output is on RC0.  This is turned on and off for each sweep.
• A trigger and marker signal is generated on RC1.  The marker goes low when output is between 453 and 457 kHz.
• The 5V frequency output is attenuated and filtered by a simple R-C network and pot.  Not very good, but it did work
• The signal is tied to a vacuum tube radio IF strip.  It's coupled into the signal grid of the converter tube.
• IF output is at the detector, where the AVC voltage is typically found.
• IF output is AC coupled into the scope channel.
• The other scope channel is connected to the marker at RC1.
• The scope display is very stable.
• The IF transformers could be adjusted to get a nice peak centered around the marker notch.

The code was done in MPLAB X.  It's ugly.  I'll clean it up a bit and post it later.