I know this is an old question but here is a quick reply.
The .35 Newton was produced in the early 1900's as a Big Game / African cartridge.
It was reported to have more poop than the .375 H&H with some loads.
The rifle that Newton produced in this caliber was about 7.5 pounds and was known to shatter the wrist under recoil.
A word of warning is in order...
Using load data that was printed that was officially printed back in the day with the newly produced powders ( such as 4064, 4320, 3031ect) can be dangerous.
Newly produced powders have more energy per grain than even 10 years ago!
The Newton line of calibers were way a head of their day gaining more velocity than most calibers could in 1913!
A great caliber to hunt with in a properly built rifle.
Some load data that was printed you may find in the #1 Speer manual, an older Herters manual but do not load straight from them due to the warning above!
Hope this helps.
**A side note, I have not looked into it yet but it has been reported that the .375 Ruger may be based on the .35 Newton**