Hi truffy,
Having messaged Howard, it sems that I did make a pattern for a compressor and sent it to him. The part was to be made in cast resin. Having been rather ill and on a lot of medication back then in 2014, some things have dropped out of memory.
If Howard recommends the Replica moulding for the compressor unit, then that is the way to go. Replica have a good reputation for the quality of their parts.
I am still modelling, though the RMweb topic on scratchbuilding building a Bulleid 2 EPB is lacking in activity, there is a topic here on building a new train set.
Colin