Here are 3 options for mounting a varient of shape center gemstones. The first option is a classic design where one round gemstone is set on either side of the center stone. This style ring can be made with your choice of side gemstones.
The second design is based on the concept two round stones will be set on each side of the center stone.
The third option is based on the concept of setting three round gemstones in a triangular shape on each side of the center stone.
336 is a style of setting that can be used for a pear shaped gemstone. Each of these designs would accomodate this style of setting.