Locking right rear wheel

59 MGA, new rear wheel cylinders, new master cyliner, drums are OK, break pads are OK, brake adjustment works fine, no damaged brake lines yet when break is pressed hard the right rear tire skids. Any thoughts

Does this vehicle use the long shoe short shoe system? Short shoe goes in front.

The shoes are the same length for each wheel.

Manually adjust both rear brakes so that they are equal.

Adjusted the brakes per manual, locked them up and backed off untill they turned. Even back off the right wheel all the way and left the other adjusted, still locked up. Also, backed off on the left wheel so there was no adjustment, adjusted the right wheel per directions, still locked up when braking.