Well I have a 247/255 in there now. Lift is not a concern at 549/571. I can't stop it from bucking when trying to lug it around. I can get idle down to about 800.
you probably have some tune-up issues that if solved would help the situation. personally i hate big cams, especially hydraulics for street cars. majority of people don't know how to tune for them, and even if your tuning skills are good there's still limitations. the more that valve timing is increased the more the engine dislikes mufflers.
