They both look very rusty, but that isn't necessarily the end of the line. Do the motors turn over or are they rusted solid? Do they both have oil? I would start by giving them both a good clean and try to assess the damage.
A title is more of an inconvenience than a job stopper. That can be take care of legally as long as the bike was never reported as stolen.
Your preference is to build the CL350, so I would follow that thought. Don't build something you aren't passionate about. Life is too short. For me the plan would be simple: a couple of boxes of SOS pads to clean up the chrome and lots of warm soapy water to wash off the years of dust and other crud. Then put the 450 up for sale with an accurate description and start working up a budget for the 350 starting with consumables like tires, cables, chain etc and then assess the motor condition.
Getting rusty old bikes to look like new always costs a lot more than we want to believe, but if you have teh time and desire to make it run, try to resist the temptation to "make it your own" and focus on getting it running well first so you can ride it.