John Cutler
Sorry I did not take any photos of this conversion.
I did not consider i would end up describing it!
If you are considering a different chassis to the Hornby one, I would recommend using the Branchlines etched nickel-silver chassis as a basis.
I have built one of these (many years ago for the old Hornby body) and it is fairly detailed without being over-complex.
I have considered using this as I have one in store.
The problem is the lack of weight.
The new Hornby body is lightweight.
So you need to at least replicate the cast metal weight of the Hornby chassis and if possible add to it.
This requires careful planning of where and how to add weight to the etched chassis; I think I will pass on that!
You also have to make the underside of the boiler and ensure it acts as a cradle for the motor.
The Rails of Sheffield Terrier specification shows a sprung central axle.
I may be tempted to try converting one………
Good Luck!