to cut slats, just measure the width of the speedport and make cuts to the width and depth of the port; then press the tape overhang down into the port. as the tape is flexible, the cuts don't have to be perfect.
yes, you can counterbalance the effect of the weight in the head by adding to the handle. i would use weight at the bottom of the yoke as an approximation of weight in the handle until you find a combination you like; then you can do to the trouble of sticking the weight inside the handle or wrapping it under the grip.