As far as the angle to offset the top slide when you have to make your own taper pins, well you are not going to read the necessary fractions of a degree off the top slide graduations.
I recently made a full set of taper pins for the change gears on my old Drummond lathe, because I did not want to wait three weeks for a packet to arrive from the UK.
Method I used was to do the math and calculate the amount of taper over one inch of length. Divide it by two. This is the amount of offset required "per side" and so is the amount the tool needs to travel outwards per inch.
Set up a piece of scrap one inch diameter bar in the lathe, turn true and parallel. Mount dial indicator on the top slide with plunger against the turned surface. Set top slide to about the angle where it should be. Set dial indicator to zero. Run the topslide along for one inch according to the graduated collar and observe the amount of in/out movement recorded by the dial indicator. Adjust topslide angle, amongst repeated mumbling, until the dial indicator reads the correct amount as per the math calculations using Pythagoras Theorem, Sine tables etc.
If you want to get real fancy, you can caluclate the length of the hypotenuse and feed the topslide by that exact amount, a gnat's whisker over the nominal one inch.
As already mentioned, once you get the right angle sorted, make the pins longer than needed at both ends, fit pin to the job and trim accordingly.
And do not POUND the pins into cast iron change gears too hard. The taper will force the metal apart until it cracks the gear. Do not ask me how I know this!! A gentle tap is all that is needed to seat the pin.