Our friend Gary Mattson of Simi Valley, California, has a fundamental problem. He doesn't want his new Optima dry-cell battery falling into the cooling fan. The factory battery tray uses a battery lip hold-down, which works well with Autolite Sta-Ful reproductions and many aftermarket batteries. But there are now aftermarket lead/acid batteries, not to mention Optima dry-cell batteries, which require a top-mount battery tray.
For those who aren't concerned with originality, Virginia Classic Mustang offers a top-mount battery tray for '65-'66 models, like those from the factory with '67-and-later Mustangs. This easy swap is accomplished in about 20 minutes and it keeps your Optima battery in place.