I think what I will do for this amp build is order a chassis and cover from Evatco to build the amp on, instead of going with my original plan of using a diecast aluminium box bought from Jaycar, Evatco stock some really nice tagboards that I could use to build the amp circuitry on, also, I've figured out that if I add one 12AX7 valve to the valve line-up, I will be able to create something like a 1 channel Marshall Plexi preamp, and still keep the EF86 valve, should be a pretty gainy amp once it's finished.
These are the tagboards/tagstrips I'm thinking of going with: