Dropped a bolt

take the head off

A magnet is the only way, if you can get the bolt align properly to allow it to come out of the hole. Otherwise you'll need to pull the head.

Rent or borrow an articulated borescope (Google to rent or buy, the scope head is steerable) (the cheapest of this type to buy is about $500). Fasten a small magnet (make sure magnet is strong enough to pick up your bolt) or a ball of something sticky like carpet tape or drying Permatex (make sure it's bound well so you don't lose it or catch it on the inside edge of the hole) on the end of a separate coat hanger wire or if possible on the end of the borescope head itself. Practice on a free bolt first. Fish carefully! If the bolt is NOT pinched at an open valve, you might hand crank the engine to move the piston up/down as needed. Good luck. Otherwise--pull the head or turn the car over and shake.

manually turn crank untill that piston is at top this might help you gain access to bolt other wise will have to remove head tough break!