Can two long calf implants be used in each leg instead of the shorter one?

Please keep in mind that a physical exam is always first necessary before providing any final surgical recommendations. Depending upon the physical exam and the patient’s goals, inner and/or outer calf implants may be necessary to best balance out the leg shape and symmetry.  Not sure I completely understand your question but patients aesthetically benefit the most from having both inner and outer implants placed that fit within the outer dimensions of the existing calf muscles.  If not done this way, complications and migration of the implants is sure to arise. 
Very few plastic surgeons specialize in this operation so you may have to travel a long distance to one that does. The implants are made of soft semi-solid silicone rubber and placed surgically through a small (3/4 inch) incision in a natural crease behind the knee. When the implants are properly sized and placed under the muscle fascia, they should blend in and look natural. There are too many critical nerves and blood vessels under the muscle to risk putting the implants under the actual muscle bellies. This too is true in the ankle area, hence not a good idea.All surgery comes with post-operative pain and recovery.  For calf implants, the first two weeks after surgery is the most difficult time because walking is painful. However most patients ambulate just fine without crutches, some choose to use them for the first 3-5 days. Recovery usually progresses at a smooth steady pace after the initial two weeks. Patients can fly back home as soon as 4-5 days post-op. Driving a car is usually allowed after 7-10 days. Low intensity seated upper body workouts can resume at 2-3 weeks, standing at 4 weeks but no legs for 6 weeks...remember, you only have one chance to heal properly. Glad to be of help. 

Calf implants come in varying sizes and lengths.  Often a single implant placed over the medial calf muscle is sufficient to improve lower leg shape. A second implant can be placed over the lateral muscle for additional shape and size. A physical examination is required. Consult a board certified plastic surgeon to answer more specific questions.