mechanical fuel pump

If the fuel pump rod drops down you'll have to take something thin like a hacksaw blade and get it back up. But before you push it back up take some grease and put it on the pushrod and then slide it back up. You'll have to work fast because it won't stay there long.

Or if you have access to the bolt on the front of the engine in line with the fuel pump, you can remove it and us a longer 3/8'' bolt and gently snug it finger tight to hold the pushrod in place. Then remove the pump. Make sure the pushrod isn't on the "toe" of the camshaft eccentric otherwise the pump will be a pain to install. Make sure you put the original bolt back in after your done or you'll have a major oil leak.

Below is a video of the pushrod being retained with a bolt. Never mind the first few moments of the video. Old fumble fingers is dropping an oil pump drive in. Then he does the push rod trick.