You may tune up Vout by taking advantage of the Rx/J/D position. Say by leaving in the LEDs you now got and add some Rx value. Or replace them with lower Vf LEDs and add a diode. Whatever suits you. Don't do such experiments with the real load connected. Use a dummy load, tune your Vref section parts for target Vout well and steady, reconnect when sure. Not to kill chips with some overvoltage set up mistake.
On the Rx pads female socket pins can be installed to easily try various resistors. To go from your 5V base up. If for 2mA nominal current in the Vref expect 0.2V additional Vout per 100Ω. If using the JFET mod probably more mA will be produced and more mV/Ω.
Yes, you could use a trimmer instead to home in. Must be arranged as a rheostat though (one of its outside pins joined to the middle pin). Plus its not easy to connect it and use it there due to its shape and pins arrangement. Maybe with small wires. Still better to be replaced with a standard resistor of near value after removing the trimmer and measuring its set value.
Yes, you could use a trimmer instead to home in. Must be arranged as a rheostat though (one of its outside pins joined to the middle pin). Plus its not easy to connect it and use it there due to its shape and pins arrangement. Maybe with small wires. Still better to be replaced with a standard resistor of near value after removing the trimmer and measuring its set value.
It needs a jumper replacement when removing that resistor. What voltage can you measure across the 100Ω ? That will tell us the mA running in the Vref.
K170BL can still work although bit forceful. Lets check if it looks genuine. Show us a close up picture of it before you use it.