It's not too difficult but care is required. First if you haven't already done so you'll probably want to order a set of estuceans (spelling?) from brownells to use, you can re-use the original factory ones, but it's better to get new ones. While your at it order the special drill bit countersink tool that goes with it, this will allow you to install them perfectly, if you have a lathe you can make the tool in about 10 minutes and save ordering one.
As far as the inletting goes, I start by roughing the grips out on the bandsaw, I generally leave about 3/8-1/2" of material surrounding the frame, more if I'm making a set of wraparound grips. I use a milling machine to cut the two level surface at the top of the grips, I also rough in the half round part at this point. The milling machine ( a drill press with a straight router bit will work) makes it easy to get a level surface that is the correct depth, but the job can be done with chisels and files perfectly too, just takes longer. Once this is done use inletting black (candle soot works) to coat the front of the frame and slowly proceed to inlet the half round area. This point is critical since it is a bearing area and if it is not done well the grips will tend to be loose. I use scrapers and sharp chisels for this job. Generally it takes me an hour or too per grip to get it the way I want it, I also make sure the backstrap lies flat on the grip pannels, a few minutes of scraping with the inletting black to show you where takes care of this pretty quickly. Once the pannels are inletted I drill for the pin. This is pretty easy, the pin can be driven to the opposite side so one of the pannels will sit flush on the opposit side. Carefully holding the pannel in position a light blow on the pin from the opposit side will clearly mark the position where the hole must be drilled. Drill the hole the same size as the pin, or even a bit smaller and do a smash fit, this ensures that the grips will stay tight when screwed down. From this point on you can drill for the screws and than trim the grips down a little proud of the frame. One trick that helps if your making flush fitting grips is to cover the frame with blue automotive tape, followed by regular masking tape. This way when you start to cut through the masking tape with files you can see the blue underneath and that should be the indication to stop. Shaping the grips is pure artistry and your on your own with that part. Here's a picture of some grips I made for my model 60. The wood is Zircote.
