I believe the 3.8 lever is considered stock for a BB applications. There is also a 4.2 lever and a 5.0 lever available. The 5.0 lever is sorta overkill for a street-car. It's considered by most a race only modification. However, If you're doing a TF-2 kit, I'd most definately go to the 4.2 lever. It just puts that much more pressure to the 2nd gear band apply. I run one in my 727 with a TF-2 kit, behind a 451, and it shifts firm but not annoyingly harsh.

Not to step on JohnRR's advice, the 3.8 will work just fine, I just think if you're gonna change it, I'd suggest the 4.2.