The schematic shows the 2 pF cap right across the antenna connector, like the small molded coil L2 which you show in your photo. I'd use a 2 pF, 500V NPO ceramic cap. To tune the amp to have the same output across the whole band, you do need to do that with a dummy load and adjust both the input trimmer and the output tuning trimmer, experimentally (while the amp is transmitting at full power, so you need a good, insulated alignment tool for this and can't use a metal screwdriver) to peak output first at 144, then peak at 148, and then set both about midway between those two peak settings, etc. I have a B3016 and it achieves ~150W output with 25-30W drive across the entire band...into a dummy load. Into my 2m vertical omni, which is tuned for 146 MHz, it doesn't -- it favors the high end of the band where the antenna is almost perfectly matched, and the low end of the band falls off in power.