difference between gt and g40 engine

[turpyboi]

seen as the g40 engine seems really rather hard to get hold of.
can you turbo a standerd gt engine.
ive heard if you use the abd 1.4 golf block you loose some compresion making room for a bit of boost?
i know conrods/pistons probs wont hold up for long but only low boost for now.
any help would be nice
thanks