its very unlikely you need that amount of Arimidex for only 300mg of test. you'll likely cause more negative side effects like low E, low libido, erection issues, low energy from running too much AI, plus you'll hinder muscle gains.
if your worried about some glands still being there from your gyno surgery and coming back, then simply run a SERM like Nolva at 10mg for the duration of your cycle (you could possibly get by not running arimidex at all)