The tall slender tuner standing up on the board is connected to the UHF antenna, the fatter shorter tuner under the copper shielding is connected to the VHF monopole antenna, so I think that pretty much shows which is which.
Sure you can test for diode action, but a more complete test would necessarily involve some method of applying voltage to the varicap diode and measuring its change in capacitance as you change the voltage.
I still think that you have a more basic problem than tuning, since you have no raster.
jr
edit add: I believe the MPN 3404 is a switching diode, not a varactor... are you sure you found the correct part?