I took a similar approach, but improved the design

I used Park's cup guides from the actual HHP-2 tool. You can find them on Amazon for $30 or so. I also used a 3/4" threaded rod (12" long) and two 3/4" washers/nuts. Plans for the future are to weld a "T-handle" to one end so I only need one wrench to use it. I'll probably weld it to the nut so the washer still has a wide surface to rest against. All-in-all a very comparable alternative to the $140 Park tool as it virtually is the same thing since it's using the same cup guides.
I'm also going to make a headset cup remover like this as soon as I can find an old seatpost that will work. My spare 30.9 post is too wide.