Your VCO is working fine, you just need to get it to proper frequency....which doesn't make sense because i can scroll from 29.999mhz on down the bands and the voltage continuously goes lower as the freq goes lower. So at 10.000 mhz, the voltage is about 5v, which is correct according to print. Could there be a typo in the service manual and it should be like 2.1v at 150khz?
Set your tuning to to WWV you know you can receive with all other setting mid point. (BFO, Fine tune etc)
Now adjust the VCO trimmer until you center WWV. That is it, you are done.
Now check low frequencies for accuracy//high frequencies for accuracy. If your reference oscillator is properly set, there will be no skewing across the range of the radio.
A note here is the VCO should hold 'lock' at 29.9999 and 150.0000 Khz.
The way it works is the VCO takes small voltage at highest frequency, then the increasing voltage 'pulls' the frequency down with varicaps.