Hi scott, 2 adjacent faces that are coplanar fragments of the same larger plane can be merged using boolean union but there isn't currently an automatic way to merge together 2 extrusions.

So for the time being to merge them you would need to delete the current fragments and then make a larger extrusion going over the full extent and then join that in.

I've attached a version where I've done that, it should be easier to fillet this one.

- Michael