Roundhouse are aware of the parts needed for this project, but here is a list and some quick snaps showing you what to expect.
Here is the HBK1 chassis kit laid out with some of the extra parts. Note that the fly cranks are the Darjeeling type (these are an extra cost). Also included are the cylinder covers and two of the three boiler bands (which should have been in the other photo!).
Also note that I requested the kit without buffer beams as I shall be using the laser cut ones from Model Engineer's Laser.
Here are parts from the HBK4 Boiler kit with the Lady Anne type dome. Note that this normally comes with a smokebox which you do not need.