I recently purchased a 65 mustang it has a straight 6 in it. I have a 289 engine out of a 64 &1/2 that I wanna put into it. Question is can this be done.
Second I also have a 88 fox body mustang. Was wondering if I could use brake system out of that and put it n my 65

 

Yes, it's done quite commonly, however, the suspension, steering, and rearend all differ between 6 and 8 cyl. cars, so it's much more involved than just the engine. I can't help you on the Fox brakes.

 

289 you have will drop right in with correct motor mounts, etc.

will need to replace the front suspension, and go to 5 lug front and rear. you'll also need a new bellhousing for your current trans.

The brakes from your 88 will not work without substantial modification.