Is this just the B1 with a megaphone? How's the curve compared to the B1?
Not sure what application your looking at. If the 2 your comparing have the same 1-3/4"- 1-7/8" head pipe and the only difference is the short megaphone muffler vs. the B1 muffler Kurt at Bassani (no longer there) years ago said the B1 makes about 1 - 1.5hp more. So pick the one you like.
Some of the applications they rate at 120hp max. They make 1-3/4" - 1.7/8" - 2" head pipes for higher HP builds.
Call and ask to be sure.