GAL 16v8 tri-state independent pin control
I am using OPAL-Jr

In Opaljr an output pin's tristate or 'OE' (Output Enable) function is specified by appending .oe to the output name. So in your example the equation would be eg.
l8.oe = l12

Most GALs have three different global modes - Simple, Complex, and Registered. In Simple mode outputs are permanently enabled or disabled, so .oe cannot be used. However if you apply .oe to a combinatorial output the compiler should automatically choose an appropriate mode (complex or registered) that supports it. In the GAL16V8 pin 11 is a shared OE which is permanently assigned to all registered outputs, so you cannot control them individually.