When I bought the bus, it came with side scoops cut-in by one of the previous owners. I wasn’t keen on them, but figured they couldn’t hurt. Besides, it would be quite a bit of work to repair.
I was wrong on the first part, and correct on the second part.
I’m pretty sure the side-scoops did let the engine run a little cooler. But, they also rammed dirt into the engine compartment every time we were off-pavement (which was often). The dusty air going into the engine surely caused more harm than running (slightly) cooler helped.
For me, this was pretty much an all-day task. Part of it included re-wiring my brother’s garage for 220VAC for the MIG.