To my knowledge, Dave has said that it is still going ahead, it depends on funding coming in from the OO models; plus he is busy with a few other projects at the moment, such as the APT and King, it would come in time.
Would it need to be a J94/Austerity? Would kit building be an option? I have seen a few kits out there, including a Peckett with a 3D printed saddle which takes a lot of the effort out of forming it.
At the end of the day, this is your layout we're talking about; don't take this as me trying to stop you or turn you away from Dave's work.