These engines are really not that hard to work on if one takes the time to read the manual and understand them. I highly suggest you get the appropriate repair manual and read it. Run-aways do not become damaging if you have someone ready with a board or piece of sheet metal to put over the intake to shut it down. Run aways with this or any motor are usually the result of a misunderstanding on the part of the assembler, again read and follow the manual.
Thew rocker arms on our 6v-53 stayed on the head because they are pinned to the lifter assembly, which is secured to the head. The rod out of the head you are referring to goes to the throttle control governor, not the fuel pump. The fuel pump is a small gear pump on the end of one of the cams on our Detroit V series engines. Each injector is fed a supply of fuel by this pump at low pressure, then the injector is pushed down by the rocker arm, acting as its own high pressure pump to inject the fuel into the cylinder.
These are excellent engines, but very misunderstood. Knowledge from experience or gained by careful reading of manuals is the mark of a good mechanic!
Regards Marti