Congrats on your new Marlin. I've read good things about Remington-Marlin 45-70 accuracy. Brownells has a good selection of peep sights. My only peep sighted Marlin is a 25-20 model 27s and it also has a beech folding front sight which in combination do a very surprising job for my 60 year old eyes. It has a nickle-sized eye piece/diopter? and is adjustble only for distance. Lee or Marbles brand. Almost what it cost for your rifle to buy new. Sometimes you see them on e bait.