If the engine has run then chances are the key was replaced during the last build as mentioned.
If a thing can't physically get into the pump, and cannot dissolve, then it's no big deal.
The bigger deal is; what if it fell out unnoticed during the sprocket-install, and the cam bolt was torqued up ok; and then, one day, 500 miles from home, it moves.oops
BTW
I heard a 7qt pan on a hi-reving engine is a great idea.
I heard 5.5 qts of oil in a 7 qt pan is worth a lotta,lotta hp.
It helped my 360 go 93mph in the Eighth.
Yeah,as a streeter, I had to build a lil skid-plate to keep it from getting smashed on stuff/ no big deal.