appearance of a 340 vs. 360

The pan rails are wider. 360 will be cast on the side and stamped on the front drivers side of the block
No, the pan rails aren't any wider(rail to rail). Just the rear main cap is different where the end pan seals against it.

All components being equal, the 360 will give you more torque & HP at less RPM too. 20 more cubes!
Looking at both side by side, 340/360, most people couldn't tell the difference & even the experts would have to looks close at the differences(block markings, balancer etc).