Good idea.. and yes it will fit in the current cage but you gotta think of a few things..
Where is the radiator going?
How much is the adapter plate going to cost?
How much is the FI computer going to run?
How much is the wiring going to cost ( about twice the amount of wiring as a VW )?
Dont get me wrong water cooled fuel injection is the way to go if its planned for appropriatley and done right.. but if your on a budget and want a fun all around beater car taht you can have a good time with the VW is the way to go.. Simple, Easy to do plus your half way there w/ the vw case mocked up anyhow.. why change it now