First, he wanted to install LPG just for economy. But I assured him, that LPG will work for full-power. So we agreed to build a performance-oriented LPG setup.
I choose KME Twin LPG reducer. It's actually two reducers bolted together. Claimed up to 410HP.
E46 has little space under the hood. And with turbo it's even worse. We have hard times positioning LPG reducer with 8 hoses to it (2 liquid gas inputs, 2 vapor gas outputs, 2 heating inputs, 2 vacuum inputs).
The only place we found was under the intake pipe
For better transient response we used plastic pipes for connecting vacuum to MAP sensor, reducer, FPR.
To maximize throughput, we installed a separate LPG valve for each part of a reducer.
HANA Blue injectors
We assembled a gas rail under the intake manifold. It's bad for maintenance, but good for performance, because injectors are close to the intake valves, and pipes are as short as possible.
Rail is fed from the both sides.
Gas outlets are positioned exactly at the center of the pipes. Ends of the outlets are cut at an angle. It creates an effect of sucking out gas with the air flow.