With regard to the bullet length difference, not the weight, what should I expect with shooting a 170 grain vs. 150 grain .30-30 factory ammo?

Nothing unless your action has a problem with max length rounds or your chamber is really short. I've had several 336 and 94's and none have had a problem cycling them.

cedestech, thanks for the reply. I have two choices of borrowed rifles. One's a Marlin and the other is a Rossi. I guess I should try both out with some practice time. I hope the Marlin works out because it has a Tang sight. The Rossi has a semi-buckhorn on the barrel.

Shoot whichever feels better to you. If they are carbines they will kick and slap you in the cheek. Don't discount buckhorn sights. My wife shoots them on all her rifles and does well with them.