I have a 1964.5 with an alternator. I want to switch it to an alternator. What modifications would i have to make

 

Hey, and welcome to the classic section of MF. Read through this stuff and see if any of this helps. Obviously, you are going to need a different bracket to hold the alternator and you are going to need to do a little bit different wiring, but going from 30 amps to 60 or more will sure help.
http://www.blert.net/comet/gen2alt/
http://www.mustangsteve.com/GENtoALT.html

 

I am in the same place you are-have a 64 1/2 with gen looking to switch to alt also. Have about decided by the time I buy brackets & mess with everything else it will be easier & also retain the stock look by going with the powermaster brand Power Gen. It is a single wire alt in the generator case. The cheapest I have found it is at Jegs-but still expensive

Jeff