Like they said cubes are everything. Depends what you want too, My littel 347" ls1 get 20 mpg on the freeway and makes 1000 hp, a 427 I would guess might get 15 mpg and make 1150-1200 hp on the same setup. My old na 427 sbc got 10 mpg on the freeway!!
TEA (TOTAL ENGINE AIRFLOW) is a very reputable and state of the art head porting company. Good bang for the buck. My motor made 430 rwhp through an A4 with TEA stage 1.5 heads and a tiny 224/224, .581 hydraulic cam. Shop around for specs and prices before you buy any head because I got a kilelr deal on porting at the time. Darts are also super cheap for the money, but I wanted a low dollar setup so I stuck with a factory head. I tried to stick with factory original parts as much as I could, it is less stressfull to beat on a motor knowing it only costs less then $3,000 to completely replace the entire engine if you grenade it! Depends what your budget is.