Warning about the cams for the ST170, they are very tricky to set up correctly, Will Pedley had a few issues with the figures he was supplied from the manufacturers, it ended in bent inlet valves, totally not his fault
The states have taken the focus and invested allot into aftermarket parts, all you have to watch out for is to not import any ecu flash products as our fuel is like jungle juice compared to theirs so the maps would be completely wrong. Most of the parts for my Turbo conversion are coming from the states.
The underdrive pulleys do help with engine pick up for sure, think the crank pulley is around 2kg lighter than the standard one, every little helps. i will be ditching them on my turbo'd engine though as if you dont have the harmonic balancer on the standard pulley the nose flex on the crank is likely to shatter the oil pump gears

Bear in mind you will have to pay import tax on them parts from the states, there is no way to tell how much, they dont even know how to calculate it, i would gess a tenner. If your really really lucky you wont pay a thing. I had to pay £90 import tax on my clutch and flywheel when it arrived.