I've got a RTAK II and had an RTAK a while back, but if I recall correctly, the differences are:
1. The RTAK had a darker coating on the blade. It was almost black, while the RTAK II has a grey-ish coating.
2. The RTAK's coating was smoother, while the RTAK II's is more of a coarser, crinkle finish.
3. The lanyard hole in the RTAK is just a tiny bit larger than the one on the RTAK II. I remember getting 550 cord through the RTAK's a lot easier than the RTAK II's.
4. The sheath on the RTAK is heavier-duty nylon.
5. The RTAK II has a pouch with a buckle closure. I could be wrong, but I'm pretty sure the RTAK had a pouch with Velcro closure.
6. The lasering on the RTAK had "USA" underneath the word "ONTARIO" while the RTAK II doesn't have the "USA" mark.
7. The RTAK II has a choil; the RTAK doesn't.
8. The RTAK has more of a clip point than the RTAK II.
9. The RTAK doesn't have the Randall's Adventure Training triangle logo.
10. The handle slabs are both lighter in color and more coarse in the RTAK II than the original RTAK.
Here's a comparison photo.
The RTAK...
And the RTAK II...