Thanks to everybody's help, not least NeilP who supplied the very clear photographs my first lipo's are now bulk charging
I replaced R55 with a 50k multi-turn potentiometer to control current, and performed the fan always on mod.
I have installed an arduino voltage / current monitor which will turn the charger off when the pack voltage reaches 49.8v (cell voltage of 4.15V if all cells are equal). Here is a photo of the Mean Well / Arduino hybrid about 30mins after I set the cells balanced to 3.8V to charge....
The grey box with the red light on it, located to the right of the fan, is a Solid State Relay which is used to allow the Arduino to shut down the charger.
Anyway, I couldn't have gotten this far without the help of NeilP and the other members which have taken their own time to post such useful information.
Please forgive the rat's nest of wires, my next part of the project is to tidy them up!