That blowback with a 45 Colt really is a problem with low power loads. My first Cowboy rifle was a Marlin that I still use frequently with loads that are frisky enough to minimize blowback. I generally use rifles in different chamberings, 357 or 32-20, that do not have that problem. I do think that I would go to a '73 clone in 38 or 357 if I were starting over. You might want to consider 44-40 if you want to get serious about Wild Bunch competitions since they require larger rifles.
My favorite is a 32-20 Marlin 1894 made back in 1898. She is sweet.
