i'm thinking of installing sholder harness belts on my 65 coupe. i now only have front lap belts (bench seat). anyone know where i could buy a complete set including mounting hardware and complete instructions? also what suggestions on back seat belts? Thanks  

Almost every mustang/parts places carry these (National Parts Depot, Paddock, Larry's Mustang, Mustang Depot, tec.).  I beleive that they carry them for front and back.  They are not inexpensive however.  

The actual 3 point seat belts are not that expensive, but if you don't have a welder and some mechanical skills, putting them in will be a great challenge for you.  The top, or 2nd point, is mounted on the edge of the roof on the inside of the car, causing you to have to peel back the headliner and welding in a nut that will accept the bolt.  If you care about the paint of your roof, you won't do that.  The convertible folks simply put the 2nd point on the pillar right behind the front seat.  That way, you don't screw up a perfectly good paint and headliner job.  Some say that will give you a back compression in case of a wreck, but my 03 Mach 1 has the seatbelt coming right over my left shoulder.  

Search on Ebay...saw a set for $39.95 plus shipping...big difference from $200 plus.