Ok fellas...318 help needed , Mpg , reliability and enough power ***for a big boat !!!

Ok ! Sooooo i bought the famous street sleepy Fury , it has a 318 ( not match ) from a 72 scamp+ a 904 , all stock, i have a A999 with a 2800 stall or a nv3500 out of a 5.2 magnum or leave the stock 904 there , 2nd i have a 489 case with sgrip 3.23 for it too , the famous question here , alway had 360s and 340s , but always heard the a 318 is a gem if done correctly , porting stocks heads ? Headers , 4bbl intake and carb, small 440ishh cam ? Let the 2bbl there ?put a dual exhaust , bla bl bla , I dont want a superstock set up , my duster is fun with its 400hp crate..but the big fury needs something respectable to have a bit of sound , performance and at least a bit of economy , not swapping to a big block ahahahah , what would be your set up if it was yours ? Thats the big question to answer !!! *** i have a 5.2 and a 5.9 magnum in the corner of my storage unit..but would love to leave this old LA in there and work it out

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