i would turbo it
given you have a mech at hand (hopefully good)
the price of a good t3, welding to exhaust
frst managment
spacer plate
head set and drilling for the t3
fuel pump frst? same fitment i expect
suitable inlet (get a rover turbo unit of ft.com easily i expect)
aftermarket cooler are cheap as chips and hosing can be made up easy
if i found a clean gti i would do it (as i have all parts laying here)
but if hes not all that then it may be a bit of a job, a simple servicing mech wont know the in's and outs, i worked in a main dealer and the guys there were haynes mechs it didnt go further than a book for most of em

shopping list
t3 turbo complete (oil feed, mani,actuator etc)
unrestrictive exhaust (magnex are good on gti's)
decent fuel pump
managment that allows turboing (cheapest/easiest being fiesta turbo)
intercooler
hosework inc charge carrier
inlet manifold suitable for turbo zetec

that would allow a bit of poke on std compression
if you then go into the engine you can low comp it in a veriety of ways (£50 to £2k! depending)

if you wanted it very simple scrap yard situation you coudl zvh it, cvh head 2i inlet (frst act) and a zvh kit would cost pennies