Engine stamping number question
 

Looking for any input or opinions on the engine number of my '69 442. The larger 75570 number appears to be stamped over the VIN stamping, but I may be wrong. I'm the second owner of the vehicle and have complete service history records and have no indication block has been replace. It has been rebuilt while the original owner had it.
I'm aware of service replacement, marine & irrigation uses but not aware of this stamping. The 'G' block, VIN stamping & casting dates are correct for the car.
Considering selling & would lik to say it's "number matching" but sure I can with this stamping.
https://cimg9.ibsrv.net/gimg/oldsmob...98b6fe970f.jpg