hay those old holes in the overflows look like they are the old style of doing things PVC pipe with fittings and you had to use O rings on both sides of the glass to get them to seal proper but they worked fine. some people when they bought one of these old style tanks setups would silicone the crap out of them and hope for the best as they don't know the old ways. Bulk heads ain't as old as over flows are. I have an older style overflow box on top of a standpipe I would prefer a overflow box and conceal the return line also. This works fine and I can make a change latter. We use to do what ever we could to make overflows work or even a standpipe for that matter. This box on a stand pipe is alright take up less real estate and my bar Gobi's have setup home right at its base the have cleared out all the sand around the stand pipe. they must like the noise of the water flowing down the pipe to the sump.

Bill