B17 is good for a bike where the bars are close to seat height. If it is significantly lower the B17 Narrow or go to a swift or swallow.
If you are more upright then the imperial (68) or the 66.
The rule is the lower the bars are to the seat the narrower you want the seat.

You need to profide the snot out of the thing the first couple weeks and yes it will take a little time to break in. The heavier you are the faster it will happen. A lot of people fid you need to start nose a little high to keep you back on the seat a little. once it starts to break in then most people level it up. Thats how both my Champion Flyer (B17 with springs) and my B17 seemed to work out. The Profide will also make the seat a little more tacky so you don't slide forward when you are cranking up the hills.