Hello all; my first post on the forum, but I do check in from time to time to search for help with other questions.

I'm having an issue modeling a certain part, and I hope that someone might be able to help me with it.  I'm trying to loft between two existing surfaces.  I know the dimensions/profile of the beginning sketch and another sketch that is at a pre-determined distance away.  I can easily loft between the two, but how do I extend the loft to the "finish" plane while following the same contour/direction/etc.?  I don't know the dimensions or location of the finish plane sketch; only that the loft should extend along its current path to the finish plane.

I've attached a similar model to illustrate what I'm trying to do.  I know the start and middle, but need the model to extend to an existing surface at the "finish" plane.