A sine plate takes up a fair bit of vertical room. And, for what you are milling there, does it really require high accuracy? A sine plate doesn't do you a heck of a lot of good unless you buy a set of gauge blocks to prop it up with. Of course, you need to know how the trig "sine function" works to make use of the whole thing
I would wonder if you could not buy an angle cutting endmill. That looks like about a 120 degree angle. I know you can get carbide insert endmills with 60, 90 and 120 degree included angles. If those are too expensive for you, there are also high speed endmills with angle grinds available.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)