winfield alloy head problem pos

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I have an on going problem with an engine , Details perchased this engine rebuilt with out a head, I put a winfield repop alloy head on it. lighter flywheel, V8 clutch, has mild cam & larger intakes, Engine ran real good but was harsh over 45mph & noisy, removed & stripped to get rebalance, found 4thou bent crank ??? straightened it to with in 1/2 thou. ran it another 200 miles, still harsh & not smooth, Sent to another pro rebuilder with another crank, they ground new crank , counter weight it, fitted cam bearings, new lifters , rings etc re checked valves & had balanced, We ran another1000 miles on still harsh, & not smoth. almost feels out of balance, Pulled out for the 5th time send moving parts to a balancer & they found very little wrong, So now i have replaced everything including my wallet. only thing not touched since day one is the repop head, engine is 100 thou over, 55thou clearance piston to head on 100mile head gasket, About to change the head but can,t beleive thats the problem, over 45 mph its noisy in vehicle, feels out of balance & yes free wheeld down hill at 50 mph out of gear & no noise or vibrations in drive line, Question anyone had problem with these repo winfield heads , any help appreciated, have run it to 70mph & it hauls nice , just don,t feel right, Haveanother sv engine that pulls 5800 revs & feels smooth. Best XMAS wishes to all on this site Derek from a very warm dry NZ.