I'm sure you already know this, but I'll put it out there anyways for those who don't.
A Buell XB motor is different than a Sportster motor regardless of whether it is rubber or solid mount. A lot of parts are similar or the same, but the mounting configuration is completely different, and really will only fit an XB (or a frame specifically designed to fit an XB motor).
Carry on.
edit: this may interest you depending where you are located, someone in Tucson was selling a Ulysses for $2000 on Facebook (with a motor).