Sounds like excessive piston to cylinder wall clearance in the engine. What is it, a 377 or a 503?
When the piston warms from the heat of combustion it gradually expands, and the noise goes away. How many miles on the engine and do you know it's full history? If it has Wiseco pistons it will tend to be noisy until warmed up.
As far as being doggy off the line, it could be as simple as a worn drive belt, improper belt deflection, or as complicated as a worn out clutch or engine. So many variables and we can't see it clearly from here. Post more details on the miles and condition, we will try to help you.
Jerry
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