You can certainly pick up parts cheaper than on K-tec but then i'm not 100% sure on courier costs.
Piper 285 with vernier pulley or a catcams cam, they prob won't need the pulley as they are ground from blanks IIRC.
Turbo i use a T25 & it cost me £550
uprated fuel pump is about £80 if you shop around
Intercooler, i'd steer clear of the grill mount personally, some say they're ok, some think they are rubbish.... up to you on that one, i made my own FMIC (ebay special for £80) & then did the piperun myself (cost about another £100-150 )
carb jets are pretty cheap, if you don't mind the car running a bit rich on normal driving then just get a grp A or k-tec carb, if you fancy having a go yourself then there is a post in the DIY section of this forum about changing jets etc.
Clutch can be had for £80-100 for the volvo(add another £170 for a paddle plate) , if you can order from a motor factors in Norway order the valeo clutch for the volvo 440 turbo in the green box.
All this is of course if you can get the parts posted by the different people & then by the time you add all the courier charges does it work out any cheaper?!
The turbo you have may be ok for decent power if it's a T3/25 of some sorts.
Headset off ebay for £40 or CGB sell them, again, not sure on courier costs, as a matter of fact Bob @ CGB may be able to supply most of the parts for you, it may be worth asking him.