"Fully worked" is a fairly vague description, but from my reaserch and own experience -
for an engine set up purely for motorsport, around 190 BHP plus you could go to 2.5 inch
strong road / occasional motorsport engine 150 - 180 BHP 2.25 inch
warm road engine - 2 inch
As for mufflers, a good sports muffler and a resonator are usually a safe bet.
Tar's for getting there. Dirt's for racing!