Very good, here we go.
The Hard part, IMO, is to set the compound properly to cut the correct taper.
Here's what I think I would do if I were in your shoes.
I would use the female taper (in the collet chuck) as a Master Reference (assuming it's in good shape).
I would hold a piece of bar stock in the 4 jaw chuck. Rough it to your best guess taper angle and turning the cylindrical portion (like the small end of the collet). In other words, the workpiece is going to look like a collet (without slots) on the end of the bar stock.
Start with the bar stock out far enough from the jaws so you can keep nibbling if the angle isn't perfect at first.
Don't forget to shorten the cylindrical end if more attempts at the taper leave the cylinder too long.
Make your finish cut using the boring bar/holder (we'll call it the Finish Bar/Holder) you will use to finish the female taper in the tool spindle.
To do that you will have to do the finish cut running the spindle in reverse and cutting on the far side of the workpiece.
That is because the angle of the taper, that the boring bar cuts, is dependent on the height of the cutter relative to the workpiece axis.
By using the same tool/holder to cut both the male (bar stock/test piece) and female tapers, they should match.
After you have replicated the collet taper and cylinder, Blue (Hi-pot Blue, not layout fluid) the female features in the collet chuck and carefully print the test piece taper.
If the test piece taper prints at the big end only (ring), you need to turn the compound (cutter end) toward the operator.
If the test piece prints at the small end only (ring), you need to turn the compound (cutter end) away from the operator.
Use a DTI against an edge of the compound to know how much you are are adjusting the angle.
When the test piece prints nicely in the Master (collet chuck), your compound is set to the right angle.
Take the bar stock (test taper) out and take great care to center the spindle in the 4 jaw.
Use other cutters/holders to rough in the female features (normal forward lathe rotation) in order to minimize wear on the Finish Bar/Holder.
If the cutting edge height of the Finish Bar/Holder changes, it will cut a different taper so take it easy on the Finish Bar/Holder.
I think I got that right. What do you think?