Doing the math:
Rise divided by run = grade
At 3% grade - 6" rise divided by .03 (grade) = 200"
200" = 16.67 feet of run
If you want 7" of clearance - 7" at 3% grade = 233.33" or almost 20' of track run to get up and over. I just wanted to point that out because it may be a factor. Maybe not, of course it depends on your available space and track plan.