The 5NHP Burrell Road Locomotives were built up on Devonshire boilers and used Devonshire cylinders, as in full size the model thus has a strong common ancestry with the Devonshire.
As mentioned the boiler and cylinders are identical, the main differences being:
All 5NHP RLs had top clacks.
They had larger diameter front and back wheels, the back wheels had 16 spokes to the Devonshire’s 14.
The shaft centres from second shaft to back axle were longer, the final drive gears were larger.
Rim brakes standard (although all later Devonshires seemed to have tem anyway)
Front tank standard.
Taller perch bracket and slightly longer front axle.
Longer smoke box
Feed pump (usually) mounts on horn plate rather than pad on countershaft.