And since you didn't get hurt take a moment to just laugh about this - think of how terrifying it was to have that big beast of a diesel engine out of your control in such proximity to you. That real butterfly in the stomach feeling is hard to replicate with movies
(I'll bet you had adrenaline shakes for a few minutes afterwards).
I agree there must've been another air source - if you could put the block of wood on and then take it off by hand while the engine was revving, there was another way in for the air. Of DD
nV53,
nV71, and
nV92 engines, a common cause of runaway was engine oil getting in the intake from the turbo (bad seal), or the roots-blower (another bad seal). Diesel's are a lean burn engine, so any source of fuel will make the fire burn hotter and the engine want to spin harder - of course having a disconnected governor or a maladjusted fuel rack or injector stuck open (fuel contamination or collapse of fuel filter) will have similar effect. Using too much d@ng starting fluid will do it too:
Just remember, don't panic! Try to close it off and back away lest you get burned