I hate the RCA 630 chassis

[Electronic M]

The VCR method should work. If the cap is rated high enough voltage, and placed in series with the injection probe you should be able to do both grids and plates. It will probably not be enough amplitude to drive the final video output.

You will at least know if it is the IF if video injection works.

The analyst may have allowed you to isolate the issue down to a single stage or component...If you plan to have more than 10 TVs cross your bench I highly recommend getting a cheap B&K analyst. They do almost everything....I dare say I could get by %99 of TV repairs with just a DMM with an HV probe and an Analyst...They are that useful (if you understand signal injection/substitution based troubleshooting).