The swap has been covered many times in many threads... research is your friend.
The rooster comb as it's called is the little peice that gives your shifter the "notches" when you put it in each gear..
That part on the mustangs is backwards compared to the mark 8.
Swapping it around isn't terribly hard, but for a person that needs instruction to "add transmission fluid" it's probably above your technical skills.
Do yourself a favor.. forget the truck trans, and forget the mustang trans.
There is too much to do for someone with little expereience to mess with, and too many places for "the unexpected" {like your evap lines, or the fuel pump sender} to give you problems.
I'm not bashing you here, so please dont get all "miffy".. I am being HONEST with you, and you should be honest with yourself in regards to your technical skill level.
a 98 mark 8 transmission is going to be AS CLOSE as you are going to get with an upgraded transmission WITHOUT having numerous places for a mistake to "end your day".
ALSO..
I know you aren't going to believe this, and I"m only gonna say it ONCE.
Pulling the transmission ALONE takes about 4 times as long as it takes to "drop the Kmember" and pull the motor and trans at the same time.
I did it both ways...
When we dropped the Kmember, we were IN and OUT in less than 4 hours.
Trying to wrestle the trans out alone {when my first gen trans failed) took 8 hours on the first day and 4 hours on the second day.
you will be doing yourself a favor by dropping the entire assembly out the botttom.
Just the "top two tranmssion bolts" alone make this technique well worth the trouble.
I will NEVER AGAIN, try to pull the transmission out by itself... there is just "too much work" in cramped spaces to make it work.
If you ever listened to ANY of my advice.. you should listen now.
The ears on the transmission will hang up on the exhaust and you wont find this out until you try to "lower the trans" out of the car. THEN your trans will be STUCK in the car.. but not bolted to ANYTHING.. a very dangerous scenario.
knowing your not gonna do it this way, means you will need to dedicate an ENTIRE WEEKEND for this job.