do a google search for "swapping a 289 into a mustang " and see what comes up.
There are a lot of ways that this can turn out to be a "money pit " not the least of which is the problem of motor mounts and tranny mounts, plus the drive shaft length and shifter linkages and so on........
Think about how much bigger the galaxie was in size compared to the little mustang's engine compartment. I know that the stang came with a 289, but do you know that there are about 4 different 289 block configurations ? And tranny choices ? You don't want to have to hack up the stang floor pan to get the trany and shifter to fit do you ?
Get some more accurate info before you do something that you will later regret............
Try the website for Hot Rod magazine to see if they ever did a swap like this in the past, so you can read about it.
Jim B. Toronto.