the yosh or akra will give you near 8-10 hp with a airbox and good map there are dynoes on rogue so built motor is not a need
i have a yosh 2-2 and jardine 2-1 replica i can possibly sell you if you are interested?
jAY HAS NO IDEA WHAT HE IS SAYING!
Hindle, erion, many others stopped making them for cost reasons. the bennies of a track bike with full are huge and anybody serious is using a full exhaust not slip-ons. the slip-on fad for the 51 and a street bike was to get some torque and HP and call it a day but the 51 likes to rev so opening the gas up lends itself to a full. i have been using a full for 8 years and could care less about the 3 hp i lose below 4500 rpms because i like the 8-10 i gain elsewhere.
the 51 lost popularity after 2002 so compaines stopped developing fulls as at that time their cost was too high for the average owner and most of them wanted starbuks systems but check anybody serious and ask some of the makers of the exhausts and they will tell you their fulls made more Hp then their slip-s
here is 11 hphttp://www.rc51.org/dyno/dmfyosh.jpg