Late A headers on an early A (smallblock)
dual exhaust with the stock 273 manifolds will work pretty good;
with the least amount of work.
If your going Racing that is not going to make as much
extra power as you want. ;)
I built a 318 and used the 273 manifolds worked good for me.
[ame="http://www.youtube.com/watch?v=Ud8mci4rjFU"]1964 Valiant dual exhaust - YouTube[/ame]