Now, let's go for a ride on Single Truck Street!
L-R: General Models Birney, converted from vibrating motor to rail speeder truck:
Corgi Birney, likewise:
Bowser Birney:
Lionel Birney, converted to 2-rail Wagner truck and working on overhead:
Stock Lionel bump and go Birney:
MTH Bump and Go Brill.
Lionel Birney and MTH Brill compared.
Bowser Birney and Brill compared. H'm. Autofocus off on that one.
Anyhoo, that should give you a feel for relative sizes.
Hope this helped!
Mitch