I would really appreciate some advice on my 67 fastback, its a 6 cylinder. i have a possible 5.3 ford engine out of a 2005 mg (zt??) it has the t5 transmision. The big question... can it be fitted? i think it is the same v8 as in the new mustangs?
any thoughts would be recieved gratefully!
allanfearnley@me.com  

My first reaction is to say no without some drastic alterations to the engine bay.  You would need to take some precise measurements from the middle of each shock tower, then take some measurements from the exhaust manifolds on the engine you are planning to shoe horn into that engine bay.  The other way to get it to fit would be to do the Mustang II front end alteration where the shock towers are practically eliminated.  Now, that is left to right fitment issues.  From front to rear isn't quite as critical as you can move the radiator support forward or back, and you can alter the tunnel to make the tranny fit.  If so, you are going to have to have some cutting and welding skills I would think.  
I haven't done this, so what I say is just a guestimation of what has to be done.  That 4.6L sized engine is a hellava lot bigger than a 289 or 200 I6.
If it was mine, I would get a 351 Windsor and put it in there with no sweat.  At any rate, you are going to have to update your suspension and rear end to accept the torque and weight of a V8.  Your current suspension and rear are very weak compared.  

Firstly thanks verymuch! I have just bought the car today! I'm planning a resto mod. So I will be upgrading all the suspension brakes etc. I think I will go with your advice and fit a block that goes in much easier! This is my first mustang, and living in Scotland advice is somewhat limited so I really do appreciate it! Is it a common conversion? 6cylinder to v8? Allan  

I6 to V8 swaps are very common. Your proposal for a late model engine is not.  You should check with the local officials for emission equipment laws pertaining to late model engines in early model cars. In California, the rule is the emission equipment must match the engine or the car, whichever is later. (so this can really mees with a swap).  

Yes, the I6 to 351W swap is about the most common swap out there, so there is tons of information and how-to's to guide you through the process. Let me know if you need any of that information whenever you make up your mind.  California has some pretty stringent emissions laws that most likely you don't have on the island.  

Allan, how did you find a Mustang in Scotland?  

i found it in birmingham! its worth the train ticket! email me if you want more info on it! allanfearnley@me.com.  

great, my mind is set now! ill go down the 351w route. i want to first order up new suspension ( coil ) and brakes. emmisions not to bad here! i have a pot of money to put into the engine and suspension now so just the choices! really do appreciate your help and any info you have!  

http://www.geocities.com/MotorCity/3573/Special/6to8.htm

I6 to V8 swap:
http://www.geocities.com/a65ragtop/VM_FAQ/mechanical/i6_to_v8.html

351C and 351W swap into a 64-66:
http://www.mustangsandmore.com/ubb/DanJonesEngineSwap.html

http://www.geocities.com/MotorCity/3573/Special/67I6tov8.htm