Firstly I am not a Mangusta owner, just an admirer.
There are going to be three typres of IR EFI available that you can build from. Two are going to be built from the TWM FI throttle bodies. One is for the IDA Weber manifold, the other for the IDF.
The third type is the Morrison (Australia) cross ram.
What you select for the hardware systems in a 'goose' probably is going to be more of what will fit best in the confinements of the Mangusta. That is including but not necessarily limited to how you are going to install the accessory shafts to the intake manifold, clearances to the deck mounted heat shields, etc.
The management system, i.e., the electronic controls are lesser of an issue. The most cost effect, but not cheap, is the Haltech E6x and harness.
Inglese Inductions offers the complete setup in either of the downdrafts with the "FAST" controls. The way they sell the setup appears to be the closest thing to a bolt it in set up that I can find.
TWM offers the mechanical components as a complete assembled "kit" without the computer. You need to pick your own "poison" for that one. Again the Haltech is the most reasonably priced electronic control system, but anything but cheap. The others like fast are just more outrageous then the Haltech.
The Morrison system is there but the entire company is very illusive and non-responsive to inquiries. That's not a comforting concept to me.
All of these companies are accessible via the internet with the possible exception of Morrison. Morrison has a web page but I guess that you need to call them. They don't like email apparently.
Hope this all helps.
This is the TWM 289-302 "vintage look" system. Their fuel rails are unique to their systems. I'm not sure if this is the IDA or IDF setup.