The R/F inner seat track is 2-3 inches shorter (up/down) than both Left sides or Right outer side are. There will be a lot of fabrication needed to convert a L/F seat track to a R/F seat track. Possible, but a lot of work. You would be better to find a power R/F seat track (40/40 with or without buddy seat or 60/40 front seats (like what you currently have in your Fifth Ave)).
Not sure what is different about it, but the Left and Right seat switches are different on a '87 M-body.
It is not hard to upgrade to power seat(s) on an M-body. In most cases, the wiring harness pigtail is already under the carpet.
Remove the seat from car (or at least unbolt it from underneath the car), pull up and can do changeover with seat inside of car (but is easier with seat outside of car - but also a bear to man-handle solo). There are four captured nuts to remove, one or two of which might be behind the exhaust heat shield. The nut size is 1/2 inch (I think) and you will need a deep socket.
There might be one or more seat spacers present (or not). If so, make note of this before reassembly. If used, they are held in place with the lock rings/clips - which sometimes are missing or fall apart. Nothing wrong with using some masking tape to hold it in place before inserting the seat.
With seat on its side (or upside down), unbolt the existing seat track from seat frame (four fasteners).
The switch bracket has two parts, inside and outside part. The two nuts are 3/8 inch (I think). You will need to cut a hole into the seat for the switch to stick through - so test fit a few times (as much is allowable) before cutting. It is SO MUCH easier to install the seat switch before the seat track.
The seat switch electrical connector (which is similar to those used for door lock/window switches) are flimsy - so use a wide flat blade screwdriver when removing the electrical connector - as well as take your time. It is much easier to install the electrical connector than to remove it - but even then, take your time. Install the electrical connector before bolting the seat track to the seat frame.
It is also good to get out a wiring diagram and test the power seat operation before installing - which can be done with a few jumper wires.
Below is a PDF file from my '87 (Front Wheel Drive) FSM - which is similar, but with a few differences.
BudW