I've changed triggers both ways. It's a lot easier to go from double to single than the other way around. You are going to have to shop around for a trigger plate that fits the dimension of the double trigger plate inlettings. In my case, there wasn't one commercially available that I could find, so I made a single trigger plate from a piece of mild steel and bought a Haynes trigger from Track. The manufacture of the plate was pretty easy using just a file, a hacksaw, and a 3/32nd drill bit for starting the trigger slot.
The inletting from the double trigger was ample, and I didn't need to remove any more wood. In order to get the proper height of trigger, I measured from from the bottom of the plate to the bottom of the sear in the non cock position, and that dimension was what I used to get the pin properly positioned in the trigger and plate tab. I initially pinned the trigger too high on the tab, but filed it down so that there was just a small teeeny tiny bit of backlash when the trigger was pressed into the inletting.
I then drilled the back hole in the plate to match the corresponding position in the original double trigger plate, and then marked the corresponding front hole where the tang bolt screwed into the plate. I drilled to centers with the drill bit entering the bottom of the plate and aimed to the center of the tang bolt head. Tapped this and screwed in the tang bolt and everything worked fine.
As you do this work, be sure to match up the trigger guard with the new trigger in order to be sure that you have adequate clearance for the trigger pull. When you go from double to single triggers your clearance will usually be good, but if you go the other way, you need to get creative with the trigger guard in order to make room and not upset the original inletting.
I'm not close to being a gun craftsman, but the project came out very good, even for a hacker like me.
Lisle George