Can someone identify what this port in the head is for?

[bugsdad]

The engine setup has a Mancini racing intake manifold and the very top edge of this port is exposed. When I was setting up the carb, I dropped a small nut in this port where the green arrow is and cannot seem to be able to dig it out. Is it ok to leave it? I can feel down in there and can bottom my finger out in the port and it doesn't seem to open up anywhere.

[brads70]

Well you found what it's for!   ....Loosing nuts and bolts !   It's just a way to save metal when they were cast and it provides some cooling foe the exhaust crossover too I guess. No worries the nut won't go anywhere. You could try a magnet?

[footin70rt]

I call it the "damn it" slot.