I ran acrossed some info I would like to share.
The engine that could be in the Lebanese Fireflies could be a Poyaud 520 French diesel.Lookin at a Argentine Firefly that had been reengined with a Poyaud 520,The exhased runs down the top of the middle of the deck to the end.Now lets say the Lebanese did this first and the Argentins followed there lead.
Looking closely at the back deck of the hull and you can tell there was some type of exhased there,from the heat stains and rust. The one thing that stand out to me is the 2 holes this can be seen cleary in photo# there could be some pipes there.I fell that there was muffler pipes there as seen in the last photo#6 the Marine on the back of the deck has his left foot on what looks like a exhased pipe.As all of us may never know but this is a real interesting thing to think about.