[EDIT 2016-09-28: It is a Kohler toilet, and the old fill valve is Kohler 81093-AA. I suspect it is the original valve. I've been in correspondence with Kohler. They asked for pictures of the toilet to identify it, which I sent. They didn't respond to my question about cutting the existing overflow-pipe. They gave model number 1138930 as an appropriate replacement, however they said it may not extend as far as I needed, so extend it all the way and should be ok. That was voicemail, so I emailed back asking for the height-range of the 1138930. Waiting for the reply.]
[EDIT 2016-09-28: still waiting for a reply to my follow-up email (but installed the 400ARHR and the project is done.]
Kohler toilet with original Kohler guts runs. It is old and is not a low-flow toilet.
Lifting the float by hand does not stop water flowing out the bowl-refill tube attached to the overflow pipe. So I bought a new valve.
New valve is the Fluidmaster 400A. It's height is adjustable, but it doesn't extend quite long enough for the Critical Line on it to be 1" above the top of the existing overflow pipe. The manufacturer did not stamp a water level mark inside the tank, though there is the water stain.
Is it ok to cut off about an inch of the overflow pipe? might need to cut 1.25 or 1.5. Haven't measured precisely.