360 into 64

Headers are pretty limited (see here: http://www.forabodiesonly.com/mopar/showthread.php?t=153326&highlight=early+headers) The other option is to keep the 273 manifolds. You might have to grind a bit on the lower edge of the head and maybe the manifold. Test fit the one for the drivers side and it will be obvious if it hits. 273 manifolds snuff up a 360 quite a bit but there are many folks running them. And then there is always the Dakota manifold hunt......

Good luck. Should be a fun car when you get the two together.