Usual modding route is
airfilter - GSR or CDA is best,
exhaust - Supersprint or janspeed,
Chip - mckrich chip or superchip,
TB - via tricker on here check for a sticky,
I'm sure that would see you around 70, also get a 75 engine and use the cam too but after all that you really should be thinking about brakes and ususpension though too.
Liam