I took myself down the shed tonight to try a few more casts.
As is often the case, it seems to me, it was a bit of a struggle to achieve the good results of the first cast, in fact the quality of none of this evening's casts were as good as the first. That said, they are all useable with work, apart from perhaps one which I took out when too soft and which has a distorted roof profile, it is the middle cast in the back row with the windows mostly cut out, the first cast is to its left and the original solid cast from three years ago is the darker one on the right.
Looking on the brighter side, I used spray release wax on the core and inner mould and it all comes apart much more easily because of this.
The buffer moulds are problematic, air entrapment in a very deep mould but ye olde worlde coach springs are highly useable with a minimum of repair etc, this one has a bubble defect in its middle, easily fillable.
Going back to the 122 cab, the parts which are hardest to get to cast are the front frames around the marker lights, I think these may need to be replaced with fabrications.
All looking quite DMU ish though
Simon