I bought a nice type 11 Stanley #4. When I received it, it had a home made lateral replacement. Needing to replace the lateral adjuster on a bench plane isn’t uncommon. (I do NOT recommend removing and replacing the lateral adjuster for ease of tuning the frog. The chance of breaking the frog is to great IMHO, work around it.)
Here is my approach to replacing the lateral adjuster on a bench plane.
I use this small anvil I picked up at a flea market, but any good solid piece of steel will work. I used and old piece of railroad tie for a long time. A large adjustable wrench can be used for support driving the pin out.
To get the replacement lateral, I drive the pin out of the donor frog. Typical the donor frog is no good so I don’t worry if it breaks. I’ve driven a few of these out, and haven’t broken a frog yet, but your mileage may very, and I wouldn’t want to try this if I really cared about the frog. Diving the pin through without grinding allows for its reuse. it un-peens it so to speak.
For the good frog, I will grind the pin off. The lateral is trash anyhow, so I don’t care if I mar it up.
I then very carefully drive the pin out. you want support as close to the pin as you can get on the back side, but clearance so the pin can move. Very light taps. Many very light taps. Be patient.
And totally unrelated, but once the lateral is removed, this is the best time to flatten the frog face. Notice the aluminum liners on the vise jaws. A wood vise can be used as well.
Then just work the pin into the hole. The file marks are from the first owner removing the original adjuster. He filed the old pin off to get it out. Why he filed from the back and not the front we will never know.
This is VERY IMPORTANT. If this is your first time doing this kind of work, read the next line 3 times or more. Now hold the frog so the pin is supported on the back side.It is very important the pin is always supported by the anvil.
Using a small ball peen hammer, lightly tap the pin around the outer edges. Did I mention It is very important the pin is always supported by the anvil. Very light taps. Use a lot of light taps instead of fewer heavy taps. Work the edge until the adjuster is snug.
And now we’re back in operational mode. You have successfully replaced your lateral adjuster.