MK1 golf 1.5 gl replacement with a GTI engine but on carbs?

OK Im sure this gets asked quite abit but I have a mk1 golf GL 1.5, the engine sucks and Ive seen a mk1 gti engine without wiring etc going quite cheap.

I understand that you can change this to a carb by the posts on here just wondered if you would need all new wiring if this was the case and if there is any difference between mk1 and mk2 gti engines at all so I can broaden my horizon slightly. Obviously I would need to change the gearbox but would I need to change the fuel tank?

Any info would be greatly appreciated.

thanks guys