When adding attachments such as Booms consider the changed net capacity of your forklift. These type accessories are typically used on counterbalanced models, so simply put anything placed on the load side side of the drive axle center linem will lessen the total capacity. This is compounded by the change in position of the load. Most counterbalaced forklifts are rated based upon a 24" load center. Fork mounted load handling devices generally put the load beyond the rated load center.
Check with the forklift manufacturer or a professional engineer who deals material handling equipment for down rating information and the updated capacity tags required by OSHA.