It's difficult to say for sure - it's apparently one of the "classic" Parker-style rollerballs that are marketed under a number of different names, with several slight variations depending on manufacturer - Ameroclassic, Classic American, Flat Top, Classic Elite, etc.
Like Curly noted, yours doesn't seem to have the extension piece that is on the Lee Valley photos, so yours is more likely one of the other variants - possibly one of the PSI kits.