Can you fit a 318 La carburetor on a 318 poly intake

The bolt pattern and carb gasket should be the same. That's going by the gasket application, which some manufacturers show being the same from 1960 well into the 1970s. A BBD is a BBD, even when it's a Holley (or in the case of my '71 Challenger, a Rochester!). They all have the same bolt pattern and approximate throttle bores.