I think the engine bay loom should be plug and play into the fuse box. Not sure whether fuel pump(s) are different. Plus brakes, front and rear suspension are different....
Tbh I would think about buying a decent ish complete GTi, swap good bits off yours and then flog your 1400. My GTi cost me £250 off ebay and its pretty good for a 1992. Also, some insurance companies have issues with 'conversions'.
As I've said before - why build something that can be easily (and cheaply) bought??