My experience is that you have the correct sender. I wonder if the head/engine was exchanged at some point for one that has the hole for the gauge sender, whcih is smaller? I know they sell reducing bushings so you can fit a guage sender in a light hole. There isn't one in there now? Aside fron that, I would think you have ot change the head, or drill a bigger hole (scary). Or a bunch of pipe fittings which would locate the sender up in the air somewhere. may look funny, but should work.
