Gregg I think you will find that weedeater motors are generally 2 stroke as used in brush cutters etc one that comes to mind is the Zenoah 26cc if I was you Mike at 72" I would go the route of one single chain saw engine of around 50cc I used a 42cc Atco in a 60" MTB and that got along a treat like nicely on the plane with a home made prop.

If you prefer it to steer a near straight course, then, YES !
one motor should be running opposite to the other, so fit opposing turn props.

If you don't, you could end up with a lot of torque steer.

A 6ft long boat is going to take some powering, whats the max rpm on the motors? and what voltage batteries are you considering.