torsen diff was an option on the blackline so some do have them fitted, you will have to contact an alfa dealer with the vin to find out but if it does that's worth having ,otherwise same as standard in every respect other than whees and trim.
CF3 a better choice IMO unless you have the money to do a swirl flap delete.
good luck with your search..
AFAIK the Blackline was not available in the CF3 engine variant as its an 07 onwards model so will have the metal flaps plastic mani combo.
if I were able to do this all again I would find one for as cheaply as possible that is a runner with decent history, say £1500, and then budget 3k to do the mods and likely required work,
don't be scared of high mileage as the lump is good and the CF3 has no swirl flaps to worry about, DO focus on upper and lower wishbones,oil cooler pipes and oil cooler,radiator,turbo and hoses and make sure there is no rust as some are jacked up on the sills and they get crushed and let water in and the car will rust from the inside out.
this is all as well as the obvious cam-belt and water pump.
just a guide a cambelt ,corroded oil cooler and some turbo hoses will set you back about £900 at a specialist so look at the car CAREFULLY!
under sealing is inconsistent on the GT,some good some not so, have a good look underneath if you can.
so buy a rust free 04-06 CF3, you should be able to do this for £1500, then budget up to 2k for work...I don't think its possible to get a decent GT for any less than 3k. you just have to decide whether to spend the money at the dealer or the garage. just remember blowing your entire budget at the dealer does not guarantee a trouble free car and third party warranty's are not worth the paper they are written on...
buying a cheaper car with some money left in the pot you stand a better chance of a happy outcome.
if 3k is a problem DONT buy a GT as it will throw up some unexpected's and as stated you are not handy with the spanners so you will be reliant on other people to correctly diagnose and fix problems. for example even a broken door handle will cost you £250 to fix at a dealer where as if you can do yourself its normally a £10 hinge and some time.
once again good luck and if you are near surrey I am happy to come and look one over for you.
this looks better than the autotrader one..https://www.gumtree.com/p/alfa-romeo...-gt/1129353486
although will need some work. they ALL will at this price point.