Greetings,
Star threads are most interesting.
Dies are 11/16-24
Expander Plug is 1/2-27
Powder Hopper thread is a strange tapered 27 TPI. (I made a custom tap for Bruce Williams to clean up threads damaged with aftermarket straight threads.)
Seating die stems are 5/16-32 for 38 caliber and smaller. For the larger calibers, 3/8-24 is used.
All taps can be purchased from McMaster-Carr. With the exception of the Powder Hopper thread. Never did find one for sale via the Internet.
If you do decide to modify the tool head, make sure the die will clear the shell plate. 38 and smaller have a 5/8" die clearance while the larger ones are 3/4".
Enlarging the holes is not a job for the drill press. It needs to be done on a Bridgeport or similar machine capable of holding the hole locations.
Personally, I would not modify a Star Tool Head. I would buy a Dillon instead.
Most of the Phelps shell plates I have seen may work with 7/8-14 dies. However, the center hole is larger than the Star 1.247" diameter and may rattle around a bit on a Star machine.
Cheers,
Dave