Not that easy. The smokebox/G8AS parallel boiler/firebox and possibly the cylinders and outside motion are directly transferable from the Fowler engine, likewise pony and trailing bogie, but the chassis frames appear different. The 6ft driving wheels are shared with the Stanier Black 5.
The tank and bunker plate work are also Stanier/Fairburn-like, without being a direct swap with either of those 2-6-4T designs.
If it had been that easy, Hornby would have had alternative tooling for their Fowler 2-6-4T ready years ago.