Do you think a pre-jowl style implant would be to masculine?

Thank you for the photos. I think your options are either a chin implant or sliding genioplasty. Both will have a slimming effect when viewed from the front so it will not provide a masculine appearance to your face. I prefer the sliding genioplasty in young people who require a greater than 5 mm advancement. Moving your own chin forward with a genioplasty allows the muscles to re-attach to your chin and provides the most natural look. 

Selecting the right chin implant is an art.  Prejowl implants fill in gaps but may widen the jaw.  The anatomic type can create a lovely tapered and feminine jawline.  For more masculine results we go for squareness.  Regardless of the type selected, they can be readily placed through the inside of your mouth for no visible scarring.

The question you are asking is whether widening of your chin (which is what a prejowl implant will do) would be concurrently helpful with increasing the forward projection of the chin. You have expressed the fear of looking too masculine and, even though that is a subjective assessment, your goal of a narrow elongated chin is incongruous with the use of a chin-prejowl implant. The combination of a non-extended anatomic chin implant style or sliding genioplasty with perioral mound/lower facial liposuction is what you seek. The lower facial fullness appeared as the buccal fat which sits above was removed exposing the residual subcutaneous fullness below it. (buccal fat removal does not have an effect that low on the face.   

 A full set of facial photographs from all angles are going to be required to make a determination about being a candidate for a chin implant.  Chin implants are manufactured in a large variety of sizes, thicknesses, and shapes.  That determination is made at time of the consultation and examination.  In our practice, we used  Implantech brand of solid silicone chin implants which are the pre-jowl chin implants. Chin implant can be placed under local anesthesia as an outpatient procedure. Digital computer imaging would also be helpful  to understand what can be accomplished with the procedure.

The way your facial architecture presents, a chin implant will certainly add a better balance to your female appearance...There are a variety of sizes or even a custom one will probably fit very nicely. Please talk to a Board Certified Plastic Surgeon that will review with you all the pertinent photographs and the aesthetic procedure involved in producing the desired result 

You have a full malar zone and a very shallow ramal/lower jawline with lower lip position that has to be considered. If you make the chin too prominent with any implant, the 'bone' will be perhaps quite defined and strong as you note. If the lower front teeth have had orthodontics (?), then you may have further review clinically to develop a proper plan. Take your time and have xrays as well to obtain the ideal approach