Some builders used a table saw for a straight cut.
I didn't have one available - I used a rough cut on a band saw with a wood blade and followed up with a large vixen file.
The whole process was not too difficult and went fairly quickly.
Since the tapering is actually optional, there is no need to work to the exact line, once it's smooth and saw mark free you can stop...
The vixen file will leave a nice finish that only needs a Scotchbrite follow up. Bevel the edges a little so you won't have to wipe away as much blood...
