wow, you must really want some work to do, ive dun a few turbo conversions on non turbo stuff like, astra gte 2.0l 8v, astra 1.7d, astra gte 16v,xr3i, and a 2.0l zetec bottom end into rs turbo with standard 1.6 cvh rs turbo head and 2 transit 2.5d, the transit was the only on that was worth doing as oposed to getin the proper turbo engine
(thats only because those engines are upto taking the heat and boost with no mods) the pistons in no turbo petrol engines are cast were as turbo pistons are forged so non turb pstons will end up with holes in due to all the extra heat, if you only run 6psi they may take it but 6 psi with the lower compresion ratio will hardly be worth the bother, but if u do go thru wth it spacer plates can work if there made and fited corectly but they will alter cam timing slightly wich will reduce power, also the crank bearing shells in turbo engines are tougher so u will need to change them but u will have the sump off anyway to fit the oil drain 4 turbo , u will also need a oil feed to the turbo( oil cooler pipes are a good place for that, if u really want a turbo omega a c20let from calibre really wud be your cheapest and best bet, it might be 500 cc smaller but it will be loads lighter and so will inprove handling and all sorts