350 engine ID with block number twist

[mdemco]

I am leaning towards leaving the SBC in my SWB project. The truck is proving to be a nice original example, and this engine was recently upgraded to a 383 stroker.

I am looking for any opinion I can get on the whether this 350 is original to the truck?

There is a twist. We have all the receipts from the engine build and the block was zero decked during its build. All the stamped in ID numbers in front of the passenger head are gone..

The engine casting number is 3970014:
3970014 350 69-77 Pass,Chevelle,Camaro, Nova,Monte Carlo 2 or 4 bolt main
3970014 350 69-79 Truck 2 or 4 bolt main
3970014 350 72 Corvette late '72,200 HP,255 HP 4 bolt main

The heads are 3973487, nothing apparently special there.

The date codes are all there, the engine is January 31 of '72, the heads are August 11 of '70 and August 23 of '71.

Does anything jump out about these dates to anyone?

I have one clue, there is a receipt before the block was machined and they stated the block ID number was "703174" this could be the partial vin number that the engine shop documented to ID the block while they had it. This does not match my vin. If that was the partial vin, I have a receipt from a year later where another shop decked the block and removed the numbers.

My SPID does not show any option for a 350 for my 1971 GMC built in St. Louis.

Any chance this motor is original to the truck?

Thanks for any input.