Get a hold of ST200 upper and lower inlet manifolds is the next mod, along with the TB as well.
If you can't get a hold of them, spend some time removing yours and clean them up, they get very gummed up in a short time.
Changed the water pump to a metal impellored one yet?
Change the exhaust, yes but it won't give a huge hike in power but it will sounds great. when you do the exhaut it's worth removing the "Y"-pipe and removing the terrible restriction in there when Ford crushes two pipes into one. Takes time, a grinder and a welder but definately worth doing for the last few bhp,