New bb build fuel economy

Thinking about building me a 400bb whid 440 crank,ending up whid 451 cui,the direction whid this build is fuel economi not performance,as this engine orignaly is a low comp engine im shooting for 9.5 ratio,any sugestions on cam pistones intake carb,this is a low budget build so cast crank cast pistons and so on,what heads are the most efficent,cast stock heads,valve angles,mild porting.....