Hi Jeff, so for your reverse engineering method, you are probably going to do the cplane method so that it is easy to draw and manipulate a cross section to make the kind of shape you want. Instead of lofting a bunch of lines to make that sloped shape (is that what you were doing before) instead just draw one side profile and make an extrusion to do it- then you can tweak just that one profile curve and the extrusion will update- that's much easier to manage for editing.

Then where you've got the vertical plane you can select your sloped extrusion, and then select that vertical plane and then run the Construct > Curve > Isect command. That command will intersect the 2 surfaces and produce a curve at their intersection, and your task will be to tweak the extrusion (by editing the profile that was extruded) until that intersection curve is the shape you need.

A couple of things that will help with this - you will want to get the 3D view to be set up with the CPlane in the plane of the extrusion curve so you can do your editing there.

But when you set your cplane up you will want to uncheck the option for repositioning the ortho top/front/right views (the options appear in the upper-right corner of the window where the options for the current command is displayed) so that the Right-side view will stay oriented along the world axis so that you'll be able to get a clear view of the intersection result.

Then the other trick is that after you do the intersection once you should select the intersection curve result and enable history updates for it by going to Edit > History and click the "Enable update" button. History updating is automatically on for extrusions, so the extrusion will automatically update when you edit its profile curve, but the intersection command does not have history updates turned on by default, so you have to turn it on with this manual step.

However, once you have turned it on then you should find the whole thing updates every time you move any control points of the original sloped extrusion piece, so you'll tweak those points in the 3D view where the cplane is at that angle, but you'll be watching the result of the history updated intersection curve in the Right-side view to see how close you are to what you're trying to get.

So like I was mentioning, you're chewing off a pretty complex task here, let me know if you get stuck on any of the things I've described here. I also did not yet do a trial run of this so I'm not 100% sure yet that I didn't miss a step or something like that.

- Michael