My 68 was originally a 6 cyl car. I want to upgrade the rear end. It has multi leaf springs and I guess an 8.2 10 bolt. What gear ratio is most likely in the car? Also wanting to put a locker in it. I see gears listed in the catalogs that I have that are listed for different spline numbers. What do I need to order, wanting to go with something around a 3.73 gear.

I most likely has a 2.73 open or 3.08 open.

You should look into the budget 8.5 10 bolt Nova rear end upgrade. It is a bolt in on your Camaro. I just finished installing one in mine with GM 3 series posi and a GM 342:1 ring and pinion nice all around gear for street use.