There are (at least) four gunwale techniques
I'll list them here from easiest to hardest. 1 and 2 below are about equal, difficulty-wise. 1) oarlock block on the inside. The photo below is Bob Lind's Honky Dory: Make a hardwood oarlock block, perhaps with a brass liner, that is tapered to the inside a bit, so it looks a little like a wedge...maybe 2-1/2" thick by 2-1/2" high by 4-1/2" long. Fasten it temporarily to the top inside edge. Or (like Bob Lind, make it longer, so you can have two holes 6" apart...in the Honky Dory this is to accomodate 2 people or 3) Cut two inwales that fit the oarlock block at one end and fit to the stem and transom at the other ends. Make a full-length outwale. Scarf some 1x2 stock together first if you have to. Fasten it all up (with glue). Don't use any spacers.
2) open spacers, with oarlock on the outside Make a full length inwale. Your oarlocks will go on the outside. Make a flat oarlock block 2-1/2" high by 1-1/8" thick by 4" long. Mount it temporarily to the top outside edge. Make a full length inwale. This can be a bit tricky because you have to fit both ends. So start with it a tad long and then wittle down teh ends, until the inwale drops into place, fitting well at both ends. Make a full-length outwale. Let it be long and run wild at the ends for now. Make some flat spacers same width as oarlock block, but only as high as the outwale, so only the oarlock block sticks down below the outwale. Temporarily mount one of these spacers on regular intervals, out in both directions from the oarlock block, maybe 12-14" apart. Make two tapered spacers. To make those, cut some stock about 18" - 24" long, same height as outwale and 1-1/8" thick. Now taper that piece so it goes from a point at one end to full thickness at the other end. Mount the tapered spacers, on the top outside edge, like the oarlock block and all the other flat spacers. but put the tapered spacers at the ends of the boat, or maybe 18" or so in from the ends. It doesn't matter. Put the outwale on to of the spacers. Clamp it up. Drill holes and install stainless bolts, washers and nylock nuts.
3) solid gunwales This is a more complex technique. This is the only photo I have right now. It doesn't show this technique well, but it's better than nothing. This technique is described in detail in the plans. It's basically one long spacer on the outside, tapered to a point at both ends, with a bunch of shallow saw kerfs cut into the inside edge of the spacer, so it can bend to the shape of the boat. The oarlock holes bore right into that double-tapered spacer. You can buy brass oarlock liners. I like to use 1" pvc pipe, which can be glued into the spacer....and replaced when needed. I sand the outide of the 1" pvc pipe. The outside diameter is 7/8," so that's what I bore into the spacer. The inside diameter is about 9/16" and you need 5/8", so you have to bore the inside of the pvc with a 5/8" twist drill. The only problem with that is cost: a 5/8" twist drill is about 30 bucks. So maybe it's better to buy brass inserts, perhaps from Jason, or Northwest River Supply or a half a dozen other suppliers.
4) Laminated I've been talking, here on the forum periodically, about 'laminated' gunwales. That's currently my favorite technique, but it's a tricky, advanced technique that hasn't made its way into my online plans yet. Laminated gunwales are made from random-length 1/4" thick strips. They're glued and clamped together in place, on the boat. You need a lot clamps to make this work. I don't have a good photo for this yet. I need to take one. ....trouble is I'm remodeling a kitchen right now. And as soon as that's done the backhoe comes and I'll start work on a new 24x26' shop in my back yard. I may not do any new boat building before the end of the summer. The gluelam photo here shows a glue laminated gunwale at an intermediate "rough in" stage, when no glue has yet been applied. After choosing naming and marking each pice the strips are layed out in order. Visqueen is taped to the inside of the boat and away the glue-up goes.
5) Ledge Top This final technique uses a lamintated gunwale on the inside or outside, with a curved 3/8" plywood ledge glued screwed and glassed down over top. The curved edge provides extra-stiffness, so you could build with pedestal seats (stitch and glue boats usually rely on a side-to-side rower's seat for absolute stiffness). The ledge also provides a a safe place (underneath) to hang rods.