You don't want 13/41 sprockets, go for 13/40... and a non o ring chain is OK, some people like them better because they have less drag...
If you have too blasters beside each other and one has a o ring chain and one don't and you give them the same push the one with out the o ring chain will roll better and easer and farther....
And the non o ring chain is like 1/2 the price...lol