Basically you have a mesh, if you're lucky it has a.bog0 and a.bog1 etc on it if not you can build a cradle for it and have two meshes.
Do you have the Blender or GMAX source? If not have a dig in the DLS for a cradle there are some around or I can build you one. I'll need to know things like the length etc.
If the B29 is in Trainz' .im or .pm mesh form then you can put its kuid number in Drivable Superadaptor,<kuid2:78193:950:1> to make it driveable. The adapter can accommodate objects from 1 m to 50 m in length and it's on the DLS.
