66' Barracuda and 273 with headers

7,000 rpm is doable with stock stuff and a 273, especially with light balanced internals. Mine was a 4 speed with 340 bell and flywheel. Not sure what it would be like with a 904 auto. I ran J heads, 340 cam intake, 340 TQ, and stock exhaust manifolds, pretty sure not even close 400 hp. But was very quick. That motor would do anything I wanted depending on gearing. Rear tires will be the trick. I'm with you on the 318. Are you porting the original 66 heads? What cam?