Help me make up my

Removing a 273 and replacing it with a LA 360. the 360 has a 480 lift 284/230 duration cam with 10-1 comp. Headers are out because it's a 66 Valiant. Using the 273 manifolds which would be the better choice? Dual exhaust or the Accurate exhaust sysyem? I am asking this for performance reaasons. I know I will have to modify trans crossmember with dual exhaust.Thanks for your suggestions