I can say with confidence that the same loading data used in the Ruger Blackhawk/Colt Anaconda/Freedom Arms/Thompson Contender are safe to use in the Marlin 1894.
The data for these handguns and this rifle top out right at 30K PSI, significantly above the rather sedate SAAMI standard maximum of 14K PSI for standard loads for the same cartridge.
The reason for the surprisingly low SAAMI maximum is out of deference for all the Colt Single Action Army (and all clones, including the Ruger New Vaquero), which are built on frames originally intended for black powder pressures.
Since the Ruger, Freedom Arms, Colt Anaconda, and Thompson/Center handguns and Marlin 1894 are of modern construction intended for high intensity cartridges, all of them can safely withstand significantly higher intensity loads.
Keep in mind, however, that the .45 Colt case still imposes a practical limit, even in its "+P" loads significantly below the .44 Remington Magnum's brisk 36K PSI.
The case walls of the .45 Colt are thinner, and the case head is likewise thinner, thus the limit.
You can still realize very impressive muzzle energy levels out of the .45 Colt that are about 80%-90% of .44 Magnum levels, but it's impossible to safely match or outdo the .44 Magnum with it.
If you want REAL power out of a .452 diameter handgun cartridge, you should skip the .45 Colt altogether and step up to the .454 Casull, .480 Ruger, or .460 S&W Magnum, in progressive order of power potential.
This all means you can also use Buffalo Bore .45 Colt and other stiff factory loads in the Marlin and these handguns.
Just make certain that your bore is clean, that the gun is in strong working order, and realize that extensive shooting of the heavy loads in these guns will wear them out much faster than shooting the more sedate SAAMI standard loads will do.
I routinely use my own medium warm handloads that propel the excellent Hornady FTX 225 grain bullet (yes, the soft elastomer spitzer bullet safe to use in tubular magazines such as that of the Marlin 1894), and I'm propelling the bullet (using W296 powder aka H110) at a respectable 1666 feet per second out of the 20" barrel of my Marlin 1894 .45 Colt.
I took my first ever deer with this very handload last November, and the doe literally fell in her tracks, stone dead before she even hit the ground!
I've recently unearthed updated loading data for that specific bullet that indicates this same bullet can be propelled at an amazing 1800+ feet per second.
The old .45 Colt is a remarkably capable cartridge, already well on its way into its second century of existence.