Col Whelen first developed the 400 Whelen, then the 38 Whelen (375 Whelen), then the 35 Whelen was developed by Griffen and Howe.
The 400 Whelen's original design was fine. The guns that Griffin & Howe produced for it had no headspace problems. It's original design was the 30/06 blown out to .454" at the shoulder and neck expanded to accept .411" bullets. The headspace problems came when other gunmakers ignored the .454" shoulder requirement and just expand the '06 case to accept .411" bullets. The case does need to blown out to have enough shoulder to headspace on. There are a couple of variants of the 400 Whelen being made today including the 400 Brown-Whelen, the 411 Howell, and the 411 Hawk, all are "improved" designs of the original 400 Whelen.
As for the 375 Whelen, there are several different variants of it, including an Ackeley Improved, a Brown-Whelen, a Howell, and the Hawk versions.
There have been several write-ups in various magazines over the years, but don't know if any are still in print. Get a copy of Wolfe Publishing's Big Bore Cartridges and Rifles or Wildcat Cartridges Vol II. I think they both list the history, developement, and several loads for it.
