I hope to understand what you want:

take a look at this part: points are not straight and,when extruded they produce a little curve difficult to fillet






i have moved these points in straight position with the rest of your shape
than extruded using tapered option obtaining a solid than filleted
then deleting a face and union all surfaces



sorry i have switched in Metric system so i did an improvisation (4 degrees tapered)
i think it works,hope you understand my example,take a look at the file attached

M

Maybe select your curve
Press TAB
and write Rebuilb
you must obtain a dialog windows ;)

Thanks to both responders. I see my mistake in the slightly messy geometry. I cleaned that up and things went as planned, after that. Consider this a lesson learned!

Thank-you,