Alpini, I don't think you have a good grasp on things. There's a difference between genuinely creative repairs processes and "just randomly cobbling stuff together"....
You seem to think that the chaos at war's end means lack of production. That's not the case.
Getting back on target here:
The G.55 used the same engine as the C.205. The C.205 was cleared for WEP even in 1943. Therefore the G.55 was cleared for WEP. There was no kit or modification, it was simply higher settings that the Italian engine (IT built clone of the DB601) was allowed to run on for a limited 5-minute duration.