Which harmonic balancer to use?

The 360 is externaly balanced. Only a balancer from a 360 will work if you chose to go with used. As for aftermarket, i like the "Pro Race" Nodular Iron balacers, they come with the option to bolt an external weight on the inside of them for an external balance. Nice product for the money. And yes you can run all the accessories on the engine... Here is a link. I have run them and like the quality, very nice product

http://www.pro-race.com/prostreet.htm