Both of those locos would make great models. Maybe Brian will continue the series of early loco builds with his Stephenson wrapping up... 
There is plenty of scope for pre-Rocket+*** locos:
The Coalbrookdale locomotive (1802)*
The Pen-y-Darren locomotive (1804)*
The Newcastle locomotive (1805)
Catch Me Who Can (1808)*
Salamanca (1812)
Puffing Billy (1813)+*
Steam Horse (1813)
Blücher (1814)
Wylam Dilly (1815)
Steam Elephant (1815)*
Killingworth Billy (1816)
Locomotion No. 1 (1825)+* (and numerous other Stockton & Darlington engines)
Billy (1826)
The Royal George (1827)
Lancashire Witch (1828)
Agenoria (1829)+
Stourbridge Lion (1829)
plus, of course the other Rainhill trials engines Sans Pareil+* and Novelty*.
+ original preserved
* replica built