i have been looking at new suspension kits for my 66 coupe that was originally an i6 but i am converting it to a 351 and the only difference i can see in the kits is the spindles. what are the other differences.

 

Besides the 5 hole wheels you need bigger brakes and higher rate springs to carry the load and put the power to the pavement

 

In addition to above,
Tie rods, tie rod ends, drag link, idler arm. And (IIRC) the pitman arm for the I6 is different as well.
So if you buy a complete suspension rebuild kit that includes all the above that would be a good start.
Then you need to think about what you want to do for steering. That extra 200 lbs puts a load on your steering, especially when you consider that you'll probably not be running 6.25" bias ply tires

Off subject of suspension, but important to note. The 6 cylinder driveshaft will twist like Chubby Checkers on a cafeine buzz, behind a 351. So you'll want to give some thought to replacing the paultry 6 cylinder differential and driveshaft as well. Besides it ain't cool to say anything less than 9" around us "good old Ford boys".

And upgrade your fuel lines, and cooling system, and....

 

I found this on ebay a few days ago it is a real good start to parts you will need I would just dump the drum brakes and get the SSBC disc brakes. If you price out all the steering parts you will find them to be well over $1000. Trust me I've made the conversion with all new parts.

http://cgi.ebay.com/ebaymotors/1965-...QQcmdZViewItem