Turbos usually respond better to even exhaust flow.
Twins don't provide that as well as an I-4.
Not that it can't be done. Honda did it back in the 80's with their CX500 an CX650 Turbos.
It was probably the better refined turbo bike of the time.
The SAAB's turbo is probably way too big to be of use, since the SAAB's engine is 2 liter or larger.
You'll need to match the turbine area ratios to match the engine exhaust flow. The turbos on the CX line were relatively tiny to come on boost at a usable RPM.