If I recall correctly the steerer tube length on the wire wheel GL triple is the same diameter as the 750, but is a bit longer, so it is not a straight bolt up.
At some point in '77 Honda switched to a roller bearing system on the GoldWing (mine has them), so even if the stems are the same length, a '77 front end might require you to convert to roller bearings. The 75-76 GL's use ball bears just like all the various SOHC4's.