My Big Bore Marlin is a .45-70 stainless guide gun with a brockman peep rear sight. The thing I liked about the brockman is that it mounted using the two rear scope mount holes, was made of steel, and had wings (a la M1A front sight), and accepted all williams aperatures.
I bought it as a deer rifle and it has yet to be put to that use. I also have cast and jacketed loads to test. ( I'm so ashamed.

) I need to get off my duff and get to it!
One thing I did also was to have a Pachmyr deccelerator recoil pad installed on it. I told my gunsmith that I wasn't a wuss, but this thing was beating me up more than I thought it should. When I picked up the rifle, he showed me my old factory "recoil pad" cut in half. Marlin basically put a plastic plate against the stock and had a perpendicular piece jutting out in the middle. This effectively focused all the recoil on a knife edge into the ole' shoulder.
Now with the deccelerator it kicks like a 20 gauge, and I can shoot it without ill effect. Now they make "pre-fit" deccelerators and sell 'em at Brownell's. (Brownell's sells the brockman sight as well, BTW.)
For me .45-70 was my choice so I could develop cast bullet loads at moderate velocities, and amped up jacketed loads for hunting. It also didn't hurt having a wealth of reloading data available for the old cartridge.
I don't think you can make a bad choice when it comes to a big bore Marlin
-Craig