There are other threads that have approached the issue of using lyman/rcbs style dies in a single stage press. most of my bullets are now PCed and I am moving away from my 450 lube sizer. buddy with a lathe machined a 7/8"-14 bolt I gave him to hold a sizing die. using a Lee push thru rod in the ram of my press. press is upside down bolted to my bench. very fast in this orientation. air cylinder for force and a collator and shuttle to auto size is in the works. Now that I have confirmed that this works well, will turn the first 1/2" of the threads to match the diameter on the lee push thru bullet sizing die. I connect hose on to this diameter down to a bucket on the floor to capture the sized bullets. the sizing diameter on the Lyman is longer than the Lee. the lee pusher does not push the bullet all the way out. I just drop a second bullet in and the lower bullet falls into the hose.
picture shows the sizing dies not all the way in. there is a 45 deg shoulder that the dies goes against with the top surface flush. o-ring has about 3 pounds of force to remove. set screw just to be sure it stays in.
I could not find anyone making these currently. My buddy said he would look at making in batches of 5 or 10 if there was any demand. Let me know if you are interested.