Glad to hear you found something that might work. If it doesn't shoot cast well I have a Winchester Trails End .357 Magnum (20" barrel) with a Williams Foolproof reciever sight mounted on it. Might be willing to talk a trade for the Marlin if its in similar condition as my Winchester; which is almost like new.
Just thought I'd make the offer in case the Marlin doesn't like cast bullets.
Good luck with the Marlin,