I've ridden Weller several times and it's not the same as Old Calaveras. Weller starts at the fire station and climbs up toward Mission Peak, as you said. Unfortunately, its not a "legal" road. There a big, angry-looking gate about a half-mile up that is usually open. I've had friendly interaction with some of the residents on the road, and they didn't mind me riding on the road, but it is an access road to the antennae on the top of the mountain. The road turns to gravel/unpaved a couple miles up but is rideable with 23mm tires or bigger. It's a great climb and is awesome in the Springtime. It's a great add-on for a lunchtime ride if you want to tack on a few more hundred feet of climbing.