You really think that will work, fitz?
Absolutely. I've done it.
Use TWO 1/4"x 4" long lagbolts at each connection. That's SIX lags for each 2x4. The lags length has to go through an 1 1/2" of the 2x4, 1/2" or so through the drywall, and 2" into the stud...voila...4". You couldn't pull it off with a bulldozer.
The lags for the bracket will only have to be 2"...1/2" for the bracket and 1 1/2" for the 2x4. They may go into the drywall a bit...but who cares? And btw. Ever try to pull a 2" lag out of wood? Ha!
I've bolted heavier things. If 2" into the stud won't hold it...3" won't either. Ha! However, that's up to you. If you feel better..hell, use 5".
Here's a tip though. Use a Studfinder to absolutely know where the edge of the three studs are. Measure from center of one outside 2x to the center 2x and to the center of the other 2x. Theoretically...it should be 16" center to center. But I've learned the hard way. Don't trust THEORY!
Once you know for sure, then you can lay out your piece lengths(theoretically 33 1/2") and holes centerlines. I usually mark mine 3/4" from the end and edge for the center of a bolt. That leaves 2" between bolts.
Before beginning, you need to look at your bracket, and make sure the Lag bolt HEADS at ANY of the studs do NOT interfere with the bracket. If so, you may have to countersink those about 1/2". The following instructions do NOT take that into consideration.
Find a bit equal to the diameter of the lag where the bottom of the threads are. Probably around 5/32" Mark and drill a pilot hole in the 2x4 for each bolt that will hold the 2x4 on the wall. Mark a level line on the wall where the bottom and end edge of the 2x4 will be. While holding the 2x4 along the line, insert the drill bit into ONE bolt hole at the end of the 2x4 and drill the pilot hole through the drywall and as deep as you can into the stud.
Now here's the key. USUALLY, small diameter bits are NOT long enough to drill through 4" of material. If you can find a LONGER than typical bit...well, cool. If not, here's what I do. You will need some help holding the 2x in place till you can fasten ONE BOLT. This insures EXACT hole to hole mounting.
Now, RE-DRILL that one hole out to 1/4" on the 2x4 ONLY. Again, place the 2x4 along the line, insert one BOLT AND WASHER in the 1/4" hole, tap strongly with a hammer, and then tighten with a ratchet and socket making sure the 2x4 remains level. Once that is done, now you can drill all the other pilot holes through the 2x, the drywall and into the studs as deep as it will go. Now, remove the bolt again, and RE DRILL all the holes in the 2x ONLY, out to 1/4". Now, go back and redrill the PILOT holes in the wall 2-3" deep as they are already started.
Now, rebolt the first location. Then insert all the rest of the Lag's and washers, tap with a hammer and tighten. Viola! One piece done.
Repeat for the other 2x, keeping in mind the vertical distance of bolt hole centers on the bracket. Vertically, align the horizontal centerline of the top 2x to the horizontal center of the bottom 2x according to that vertical dimension of the bolt hole centers on the bracket.
Once they are up, figure your distance to the midpoint of the width of the room. It may NOT match the midpoint of the 2x, as the center stud may be offset a bit. In fact, I'd almost bet it is. Now you have a centerline to mark your holes for the bracket. Once you have those marked, either by simply raising the bracket up and holding it in place, or by measurement, drill your pilot holes. But frankly, I'd use the bracket itself to mark the holes. That way, you are DEAD ON!
And then, do the same with the bolts for the bracket. Tap them in lightly and GET ER' DONE!
And btw...the REASON I drill pilot holes are two fold. One, it makes tightening the bolts easier, especially if you hit a knot, and two, it keeps the 2x from SPLITTING...yes SPLITTING! I've seen it happen. 2 bolts, with no pilot, can potentially split a 2x. One other thing. Some people will find this a bit overkill and time consuming. Well, it all depends. I say...can you afford for your monitor to fall?
Nothing is easy. My latest project is no exception. So far, it's taken six months to design, purchase, demo, build/re install. However..I'm so close to finishing it I can taste it. Hopefully today!!
Good for you! Had I known the bracket looked like that..well, I probably would have done it differently than I said. Oh well. Looks good Myriad.