Alllllllllllllllrighty. So just picked mine up yesterday, and spent today fitting it to a Boyd's walnut stock. Not surprisingly, I experienced some problems. Here's what went down:
As you can see, the gas vent hole and the supplied third mounting hole do not line up at all. I expected this, and had a solution prepared...
Does removing the third mounting point weaken the rail? Yes. But I'm betting that two fasteners will be enough to hold the rail on place, given that's all that held the old sling in place. Also, I'm not a fan of plugging up that vent hole. It might not be 100% necessary on a semi-auto M1A clone, but I'd rather have the vent hole than the third mount. Also, for anyone wondering if they can do the same, take some solace that Sadlak only mounts their stupidly expensive rail with two bolts as well. Coincidentally, had the vent hole lined up, I had planned to bore a hole down the inside of the supplied screw in order to allow for some degree of venting. So on to the next problem (and terrible photo).
Here you can see possibly the most frustrating part of the whole installation: a gap between the mounting pad on the rail, and the corresponding mounting position of the stock. I surmise that this gap exists merely because the Boyd's stock is damn fat everywhere else except that mounting pad.
Ta da! Some quality time with a belt sander and a piece of brass yields a nice wedge that won't corrode nor react with the aluminium rail nor the steel cap screws. Speaking of screws...
The supplied cap screws are quite nice, but are counterbored/flathead in design. The notion of torquing their tapered heads into the walnut alone made me cringe (even Norinco used washers to spread increase their rivets' bearing surface!) so I fired up the lathe and made a pair of brass inserts that fit into the washer-sized divots Boyd carves out of their stocks. The inserts are lazily chamfered (used a drill bit) in order to keep the screw flush with the surface of the stock's channel.
A quick trip to the sandblaster, and a coat of high-temp paint (which matched the anodizing better than I ever could have hoped!) and I now have a rail. As it sits, the gap at both the front and rear is uniform, and it's straight as an arrow. If you didn't really look too hard, I doubt you'd even notice the spacer. Also, as a quick aside, I too found the supplied hardware too long so I used the gas-vent-hole screw in one position, and cut the other down slightly to fit.
Looks a damn sight better than it did, and it'll look even better once I have my GG&G bipod mounted up there!
Oh, sorry, what was that you were saying? You love that Smith Navy brake, too?! Well, it just so happens I'm selling a couple more that I'm not using! *end shameless plug*