Could be one in stock somewhere.

That's possible, but if there is one in the system, those sites will usually do a search for it and that option didn't come up. If someone REALLY wants one, they would need to call a dealer and have them search the system.

I believe most of the Yenko blocks were used in Can-Am racing ..

Since this is a complete motor, with a early Yenko block, would I assume it came out of a car Don had replaced the motor with. Did he sell complete motors in the 70's. My gut tells me this could be a late 68 or 69 motor but will search for some identification on it. It just has all the parts from a full motor that Chevy would have put in the ZL1 except it has the Yenko block. So little information out there. I have also been told so many different things. Thanks

What’s the casting date of the block and the heads?

It is not a 69 block.
Don had those Yenko blocks cast in the mid-70's.
GM did not let Yenko used the molds in 69 - the blocks were still in production.

You seem to have included a picture of your Trans Am's original Pontiac 400 cid engine casting number 481988 XX, which confuses matters.