For your conversion:

1) The seat bottom is the same for fold down or not, so the one you have will work just fine. Providing you are starting with a car that does not have the rear fold down seat option and you want to add this option.

2) Remove the seat back and bottom. The tangs that hold the non fold down seat in place will have to be removed.

3) Coupe vs. Conv. are a bit different in regards to the rear fold down seat. The conv. model is a bit narrower so be sure you are buying the correct one for your application.

4) Parts needed for a complete fold down rear seat:
a) Fold down rear seat frame, be sure all of the following are present if you are buying one. Frame, hardboard back (this is what the carpet glues to) and three trim pieces that go at the top of the back side of the seat. In other words, when the seat is in the "down" position, there is a center trim piece and two corners (ends) that will be facing the front seats at the top edge of the carpet. If they are not there, you are screwed, they are not repopped! The carpet is repopped & available.
b) There are also a pair of hinges. THESE CAN BE TOUGH TO FIND as they are not repopped and most likely no one would sell them seperately. Hense the reason I had to buy three seats...
c) Floor brackets ARE repopped and can be welded or bolted in place. I welded mine. They weld to the floor under the seat and receive the hinges as the seat is being installed.
d) You will most likely need a new package tray, they are the same for fold down or non fold down and they are repopped.
e) You will need the vinyl rear seat seperator. Screws to the webbing behind the seat and is exposed when the seat is folded down. Repopped and available.
f) Retaining latch, (67 used clips on both sides) and they are repopped. 68-69 used a latch (repopped). The knob is repopped for this latch as well (same as for your seat adjuster lever I beleive).
g) Rubber bumpers that the seat rests on when in the upright position. Repopped and available.
h) Seat seperator "gutter". Part that gets tack welded or screwed into place and receives the vinyl seperator in part (e) above.
i) Plastic cup for the rubber bumper on the driver's side. Hard to find as someone repops them now and then. Terry has one for me (thanks buddy).
j) There is also a post that screws into the left side of the fold down seat, this post is basically a striker like on the door jamb of your car. It catches the latch on the 68-69. Remember 67 uses a "catch" on both sides, not the latch type. This "striker" is NOT repopped and could be tough to find. Hense the reason I had to buy 3 seats to get one complete.
k) Rear fold down seat cover repopped for standard and deluxe interiors.