does anyone knoe approx how many amps the engine cranking motor draws

The factory specs call for 110 amps max at 10 volts, unloaded. This is really dumb, because if the starter is unloaded, there will be 12 volts available. They say to use your handy dandy carbon pile load bank to load the battery down to 12 volts. That is silly, of course.

I am sorry I can't give you a real world measurement, as all four of my Chevy engines have geared starters, and draw much less current than your direct drive starter.

So, I will have to trust my failing memory and say 300 to 400 amps when cranking a 454.