best way to make it breathe

My take - The probelm with factory heads is the cost vs return. The iron RHS heads are fairly inexpensive, and the EQ Magnums are even more so. Both of which are capable of equaling or exceeding factory LA based as-cast flow. The cheapest set to do would be a set of "596" LA heads - found on later model LA 360s. They use LA intakes, LA valves, LA springs, etc, and have a very good exh port vs the earlier stuff. Beyond that - they are all pretty much the same and by the time you have a perfomance shop complete the machining, exh seats, new valves, springs, retainers, and locks, plus doing guides and milling, you will be spending within a few hundred od the RHS heads, and slightly more than an assembled set of EQ Magnums. Plus, with LA heads you lose the possibility of building a modern engine using quench for power and pump fuel.