Gas Tank Modification

I am trying to adapt this tank to a Classic.  The fuel fill is a copper 1.5" NPT pipe that was supported by the old tank and simply extend through the deck and had a threaded cap.  This tank has the modern 1.5" OD inlet which won't work with the 1.5" NPT and does not align with the hole in the deck anyway.  The hole for the sending unit does align.  I'm thinking of removing the sending unit and installing a floor flange that will accept the copper 1.5" NPT pipe.  Only problem is that a copper floor flange is more expensive that the tank. Cast Iron is much less expensive. Can a copper pipe be connected cast iron fitting?