Can someone explain this port please
Just look at the bottom of the intake in the pan rail area. If there's not a hole for the locator pins in that area, then you'll have to remove the locator pins. They're only there to keep the gasket from moving out of position when you install it. Just glue it to the block before dropping the intake on. Or you can do like some and just use rtv instead of a gasket. Personally, I prefer using the gasket.
By the way, that fitting you have for the hose from the intake to the water pump is too long. Reproduction fittings are available for a very modest cost. Two different sizes, depending on intake and what size bypass hose you run.
Mopar Nipple 1" BYPASS for 1970 & Later 318/340/360! *See FITS & DETAILS Below! | eBay Mopar BYPASS Nipple Hose 3/4" on 1965-1974 Small Block! *ALL FITS DETAILS Below! | eBay
Early 273s used a smaller diameter bypass hose. Your intake probably uses the larger, later version. Most rebuilt cast iron water pumps today will take the screw-in fitting for the larger bypass hose, but will have a threaded adapter to run the smaller diameter fitting. If you're running the later aluminum water pump, the fitting is built in and it will require the larger bypass hose.