If your using your speedo then its not accurate at high speeds.

Anything that creates more power in the very top of the RPM will help. "big" Pulleys kill top end power on very long pulls.

As stated Intake manifolds and a dump exhaust will help. Any porting/matching, polishing type stuff helps in the very top rpms.

I broke 180(based off of speedo) with a 178 pulley but dear god was it a long pull. after 165 you can count each MPH slowly . It was a 1 time deal and i probably had a good tail wind helping me. A good tail wind helps a bit.