Best thing you will ever do is get rid of those darn shock towers. But if you really want to be different and you do not want to get rid of the shock towers you can put a 2.3 turbo in a 67-8. It will almost bolt right in. a 65-6 is narrower then a 67-8 so I had to remove the shock towers to get the 2.3 Turbo engine to fit where it looked like it was stock. What other engine can you put in a early mustang and get real close to 30 mpg and have 300 wrhp?