I have a 67 soupe that currently has the stock 289. I know that the 67's came with the 390 as an engine option and was wondering how difficult the swap would be to the 390, i.e. mods to the shock tower etc.

 

I think the 390 will sit right in there. Because the engine compartment was the same size on all cars, whether it be a big block or small block. You probably have to change the bell housing, and maybe the motor mounts.

 

No shock tower modifications are needed, however.... You will need a C6 with an FE bell pattern. You'll also need a C6 tranny cross member. Your small block frame mounts can be modified to work with a big block by drilling a new hole for one of the bolts. You'll need big block motor mount isolators and block adapter plates. If you want to run cast iron exhaust manifolds, you'll need 14 bolt hole "GT" type heads and exhaust manifolds specifically designed for big block Mustangs or Fairlanes. If you plan to run headers, you can use standard 8 exhaust bolt heads. In addition, you'll need to address your cooling system, suspension and rear end. My car was converted from a straight six a long time ago. The guy fabricated alot of the parts like the frame mounts and the tranny cross member. I'm in the process of putting all of the factory parts back in the car and I've found most of the stuff on Ebay. The cast iron manifolds can be a challenge as they seem to get sucked up by guys building concourse correct cars. Hope this helps.