Bob F,
It's the 'based on' that worries me. I believe there may actually be two 350 G&H Magnums ... an improved version the dimensions of which are given in Ken Howell's 'Designing and Forming Custom Cartridges' and erronously named as the 350 G&H Magnum (dimensions like a 35/8mmRemMag ... I have heard of a 350 G&H Magnum Improved) plus the 350 G&H Magnum which is indeed simply a 375H&H necked down to 35cal ... these dimensions being pretty much what Cartridges of the World provide. The 400Whelen was also 'based on the 30/06' but the shoulder diameter was the fly in the ointment to anyone that simply opened up a 30/06 to 0.411". Not sure whether the 350 G&H also had subtle differences, but she'd be a sweet heart feeding and surely worthy of a resurrection to a 35cal nut like me.
Cheers...
Con