I don't think there is any difference as I put a Chebby 1 in my 55. Did you try testing the wiring and gauge? Disconnect the wire from the sending unit and observe the gauge. Then apply a ground to the lead and heck the gauge again. Can't remember if open or grounded will cause full deflection. If no change I figure you must have pinched the lead from the gauge. If you're in Winnipeg I can let you try out my sending unit as I went to a fuel cell.

Oh to test the sending unit connect your VOM to the sender and the ground strap of the sender. What is the resistance? If you remove the sender from the tank hook, up the VOM again, and you can lift the float up and down to check that the resistance changes.