The slot faces rear on the old style big twins; I'm not 100% sure about your 40hp. The main thing is, the bolt holes have a threaded side and a side that's drilled larger than the bolt thread, so it will clamp when the bolt is tightened. Naturally, the drilled larger side must face the direction the bolt comes in from. Other than that, whatever allows you to access the bolts most easily.
I find it easier to get at the clamp bolts if their heads face directly outward. Anything else, and it's too hard to remove the upper bolt without dropping it down the exhaust housing.
Sure...go ahead and laugh at my old aluminum boat. It's paid for!