I don't know if I'm an expert and I did "flunk" the first go at it, but I'm happy to give you my 2c on making a wood mast.
The picture below show two halves of the mast before final glue up. My mast has 7 segments while yours will have only 4 but I think you can just imagine as if it was 4.
To taper the mast, I first formed the halves as if it was going to be a straight mast then I took a saw to the half that looks like a U and cut it where the mast is suppose to start tapering. I then planed (or sawed, don't really remember) the vertical sides down of the tapering piece to the taper I wanted. I did not touch the V half of the mast, the one with the luff groove that I believe should be straight.
Here is a picture of the lower half front portion which is straight.
The pin joins the straight portion to the tapered portion and also serves as reinforce this area which is where the tangs attach.
Whala here is the upper part of the mast with the tapered front.
One thing I should tell you Louie is that make sure you put a lot of good bracing if you are going to use lap joints. Unlike birdsmouth joints, lap joints are not self aligning. With these birds mouth joints, all we really had to do was to make sure all the staves where bound together well and the mast self aligned.
With the mast you want to build I'd do the following. Use 90 deg birdmouth joints so there is some self alignment. Taper the front only along the wider staves. The front piece seems like it should bend to the taper no problem. To do the tapering, use a saw to rough cut it to shape and then use a plane to get it to final shape.
If you like and have some way of getting the materials and finished mast to and from my place, you are welcome to built it there.