Before I would recommend anything I would need more info.
What is your current Body fat percentage?
What is your time line for 3-4 pounds of muscle?
Do you have a diet set up that will support 3-4 pounds of additional muscle on your frame or are you just thinking a magic pill will do the work?
What is your current exercise routine?
3-4 pounds of muscle really isn't enough to really justify PED's unless you need to lean out cause your body fat percentage is high. A good surplus diet and hard work at the gym can get you in the right direction. Now if you have already been doing all that and are looking for a boost to push your body out of its happy zone, PEDs can help with that as well.
I as an individual am not a fan of SARMs as human trials have not even been approved on these drugs and everyone pushes them as a "safe" alternative, when they can't point to an actual human trial performed in a controlled environment that proves that SARMs are any safer than say Anavar or Primo. Yes, I used SARMs till I really started to do my own research and stopped relying on my Bro's for all my info.
If you really decide to jump into the world of PEDs, I would recommend Anavar at no less than 5 mg a day and preferably 10 mg a day taken in 2 5 mg doses 24 hours apart. Make sure to test any Anavar you receive, they make tests to test it at home.