Gearfried the Iron Knight destroys equip magic cards when they're equipped to him, and fusion sword murasame blade says it's not destroyed by effects that destroy magic cards.
So if I equip the fusion sword to gearfried will he be able to keep the equip and get the 800 bonus? Since his effect can't blow up the sword?

Correct, the effect of "Gearfried the Iron Knight" would not destroy "Fusion Sword Murasame Blade".