As someone who has built some masts (including some 1:1 scale ones), I can offer some observations.
One, do not start with a round dowel.
This is totally counter-intuitive. But, very few dowel out there are straight, and the few that are seldom stay that way. For another, masts taper, some less, some more, but all do. Lastly, 'round' masts need all sorts of flat places to attach things to. On a round dowel, flats are made by subtraction, which gets to be a pain, as the round dowel wants to roll around.
What to do?
Old, old, trick--in Ship Modeler's Shop Notes--is to make a jig. A 14-18" long 1x4 will work. This needs a 90º V groove down its length. This should be about 1/4" deep. A 90º bevel cutter in a router, or two passes over a table saw will work. A metal pin or a tiny screw in one end of the groove will serve as a stop.
Then, you get some square stock a bit bigger than needed, and a hair longer than required.
Lay the stock in the groove and plane the corner that is exposed. Rotate and repeat, you have an octagon. This can be repeated to make a 16-sided shape, which cant then be planed to round.
Now, the clever thing to do is to lay some paper tape along the jig, and mark out the lengths needed on the tape. To get real spiffy, spot things like the cheeks for the cross-trees . Take the razor saw and carefully saw down to the depth, width, and,--particularly for America--angle of the cuts. Pare those off, and file flat. Square stock is very nice for laying out and boring holes for sheaves through the mast, too.
With the "bits" cut out, you can then plane a taper in., one flat at a time.
This can be very satisfying work, and the results show.