Your right, the 3 and the 5 LNB dish is the same.It seems I had assumed that the SL-3 dish was smaller than the SL-5. I just checked solidsignal.com and the dish itself is indeed the same size. Still, the single combination LNB would have given for a neater appearance if I really do not need the 110 and 119 locations.
As for the LNBs , the ones I've seen are 1 piece units.