Bowhunter
It appears that you are not asking for our opinions. You are asking for us to validate your decision. You have already made up your mind to go with the .45-70.
A long barreled .357 mag is an absolute joy to shoot, very accurate, much cheaper and easier to reload than a .45-70, much quieter, much easier to shoot accurately in any rifle (less blast, recoil, etc.), vastly cheaper for factory ammo, and will easily do the job on varmints (including coyotes) out to 150 yards. The .357 mag is plainly the better choice here. The concept that a 400 grain chunk of lead, almost a half an inch in diameter, is a better "varmint" round, is in my opinion incorrect.
But, shoot what makes you happy. :-)
Regards,
Mannyrock