This is based on a design that was never built.
The Bulleid Merchant navy went through various designs before ending up with the loco we have now.
These were design for heavy express train duties, which the first 2 designs were a 4-8-2 and a 2-8-2.
I chose the first design as a couple of 2-8-2's exsist in 4mm.
This is a revised version of the first chassis, and now has voids in the chassis to fill with weight (Liquid gravity) to keep the weight low down.
You will need part 2 to complete.
https://www.shapeways.com/product/XP996PSSA/revised-bulleid-chassis-parts-2-2?optionId=64187764