I have an edge 540 with the dl 50 and standard standoffs. I have about 1/2 to 3/4 clearance and no trouble here. I would not cut hole in firewall unless i had trouble, first mount the engine and try it. Then if you have trouble cut hole or baffle the cowl.

I do not like the holes in the firewall for the fact that fuel will get into the inside of you fuse. And soak into the balsa. I have several engines and all of them would do it. the only ones that didn't was the side draft, because they are side draft carbs.

Just my 2 cents