Ok, while I may believe in low carb bulking, there are a couple of points to remember when trying to gain lbm, regardless of what type of diet you do.
1) protien. Amino acids are the building blocks of your muscle tissue. You need to take in large amounts of complete protien to gain lbm at a rapid rate. Incomplete protiens do not count. I would say 1.5 g of COMPLETE protiens (don't count vegetable based protiens) per ibs of bw.
2) calories. It takes alot of calories to fuel intense training and feed a growing body. It is also metabolically expensive to build new muscle mass. If you are not getting enough calories to handle all of these needs, all of that complete protien you are eating in point #1 is a waste. Much of it will be burned as fuel, and will not contribute to gains in lbm.
3) meal frequincy. Never go more than 3 hours without eating when trying to put on size (other than sleep, however getting up and eating a small high protien meal in the middle of the night would be a good idea). That means at least 6 meals a day. 9 or 10 is better. Higher meal frequincy not only ensures that you get a continual intake of calories for fuel and protien for building new tissue, but also keeps your metabolism higher and blood sugar levels more stable, which can help reduce gains in bf. Also bear in mind that if one consumes 10+ meals a day, you can eat smaller 500 calories meals and still get over 5000 cals a day. By eating smaller meals in one sitting, there is a much lower chance of extra calories spilling over and contributing to gains in bf.
Of course there is much more to gaining lbm than your diet, but that is beyond the scope of this thread. Just remember nutrition, training and rest are all of equal importance for putting on size. If any of the 3 is lacking, it will severly compromise your progress.