Diesel 6-71

Not that lever. This lever does not load & lock.
Your thinking of the blower shut down flap that this engine dies not have.

If you're going to start a Detroit that hasn't been run in a few years and doesn't have an e-stop make sure you have some means of blocking the air supply if it starts up with the rack stuck wide open.

There ya go, Sisters to what our Bertie has, 12V71TIs.
Don't get much better that that.
71s rule..

After any work, I'm down there with the engine at start ups.
I usually have a good vice grip on that governor shut down lever.
And, as you mention, some way to shut off the air to the blower. Not a towel or cardboard, 1/4 min plywood.

On this, I'd probably want the valve cover off to check the rack and ensure no exhaust valves were stuck down.
While your there, it's easy to crack open the last injectors fuel in line and help prime the injectors. May help save the starter and/or battery.

Have some fresh CF-2, 30W and Marvel Mystery oil ready also.

30W for the clutch and engine.
MMO for the engine and clutch. Also fuel injectors, exhaust valves and rings (added at the fuel filters).
And yes, 3in1 oil for the Fetzer/gizmo when applicable.

On an old thread this question came up. Not sure how I answered then but I'll try my thoughts here.
My diesel mentor advised me to pour a bottle into a Racor fuel filter to help out on a poor running 671 that had sat up a while. Much later, I think he meant a little bottle.
The smoke blocked the sun for several minutes. I remember taking turns with another guy, fire extinguisher in hand standing over the running engine while I walked up the dock out of the smoke, told others it was o k (no fire) and went back to relive the other guy on fire watch so he could go get some air.
When the smoke cleared, that engine settled down and purred like a kitten.

Old Detroit injectors are a beast to them selves. Rotating barrel valve, mini rack, mini filter, plunger, sleeve barrel and patterned tip.
One lil spec of crud can mess up these and more, just a gizmo that fits in the palm of most hands.
MMO also gets down to the piston rings faster also (IMO).

My DDC mentor (Henery) told me that he had already tried atf, and all other snake oils and he preferred MMO. That was over 30 years ago.
I have tried nothing else.