I love my Camp Carbine...
That said, we have all grown to enjoy the Modularity and ability to Customize the 1911. Afterall, it's what has made it the most popular Combat, and Game gun ever produced.
As a result, IMHO, the BEST long gun that compliments the 1911 is the AR-15. The AR is a versatile weapon that has improved through years of Military use, much like the 1911.
The AR provides a basic foundation which allows the user to personalize it for the Mission at hand. It can be had in long and short versions, and can be easily swapped between them... In fact, you can configure it use pistol caliber's, and if you're looking for the BIG, heavy calibers, well, Tony Rumore has some really cool alternatives, the .458 SOCOM is proably unrivaled.
While the 45-70 is a fine animal, I would contend it matches up better with a 45 Colt in a SAA than the ubiquitous 1911.