Converting a 1967, 6 cylinder to a V-8 can be an expensive proposition unless you do the work yourself.  These web pages tell you what is involved and where to find it while staying on a shoestring budget.  Certain parts simply MUST be changed to cope with the added power and weight of a 351-C engine.  Other changes are simply desirable for practical reasons. 

You  MUST change: 

351 C Engine Engine Mounts Front suspension Drive Shaft Differential Rear Brakes (With the new differential) Rear Wheels (From 4 bolt to 5 bolt) Exhaust System Miscellaneous brackets and linkages

NEW Frame Based and Updated.....change you bookmark to http://home.comcast.net/~jelerath/mustang/main/master-fr.html

Other possible MUSTS: 

• Radiator
• Transmission
• Transmission Linkages

• Transmission
• Front disk brakes (these will actually stop the car and give you a 5 bolt wheel pattern)
• Distributor
• 11" Rear drum brakes (From a 9" Differential)
• Large diameter front anti-sway bar
• Rear anti-sway bar