OK
Pretty sure there is no way to easily mount a conventional "leaf" type rear sight on the new Ruger .44 auto. The rifle comes with a factory peep mounted where most peeps get located, at the rear of the receiver.
A "leaf" at the rear of the receiver is odd and would be extremely difficult to shoot accurately. Ones eye would not do well trying to align the leaf, blade and target w/ the leaf so close to the eye. The beauty of a peep is you look through it, not at it, forward to the front sight. A leaf rearward would be counter productive, as you seem to have found out.
I can relate to not seeing the front sight on peep sights like you'd like. On short sight radius rigs, (like an M4 per example) I do not see the front post like I used to.
The easy answer is to scope your Ruger Carbine. It comes with the std Ruger scope mount notches on the receiver. A set of Ruger rings of the correct height will not be hard to find (it may take two separate heights fore and aft). A low power scope will be a boon for your shooting, honest.
That is a heck of a carbine by the way.