i just had engine 383 stroker engine built by machine shop(with aluminum heads)...machine shop ran engine on stand and ran great.i installed engine and engine runs rough and tach does not work.i checked all spark plug wires and everything is correct(correct firing order) i had 2 ground wires on rear of engine that were grounded from valve covers to firewall.i changed ground from firewall to rear of engine(due to not wanting to ground to aluminum heads on valve covers)could this be the problem?