Can anybody tell me if the Nelson glow plugs are the standard glow plug thread size? In pictures I've seen they appear to be larger diameter.

Yes.  They are of a bigger diameter.

Also, they do not bottom out against a plug washer, but rather use a cone at the bottom of the plug that seals against a cone-shape in the head. 

This design has become the new standard of most high performance engines.  The current crop of plugs requires a 10 mm hex wrench.