I have something that was told to be a similar Chevy CanAm block. It is in my 427 (well 468) Cobra now, but it has been polished and missing all the numbers. I have had it around 10 years and I got it from a guy that got it from another guy. I think another fellow said that it may be the same castings but done post the CanAm Chevy block era by somene besides Chevy (all fuzzy). My block does have sleeves and a boss for the mech. pump. I think you can see some photos in the CHEVROLET POWER BOOK from many years ago that list all the various combination, Lined, Unlined, destroked with 348/409 cranks. I think also the oiling system over the filter area may be slightly different the the 4 Bolt BBC's but not sure.
I think it may have one casting number over the bellhousing boss and I'll look and see if I can see it, but NO GM/Winters Snowflake or anything left after whoever owned it polished it.
http://www.gtsparkplugs.com/VSECobra.html scroll down and you can see some fuzzy pics on the dyno and stuff in the car.
While the car was at VSE in Carmel Ca, a guy came over and flipped when he saw the block and said it was a CanAm block as he was right in the midst of a restore of a vintage CanAm car (McLaren?). Again, not sure if he really knows or not but he mentioned the oil taps at the top of the filter house as being unique. I offered it up in trade for an alloy SBF as 700hp in the VSE is out of whack even for me, but he was car rich and cash poor. So in it stays.
BTW I also have somewhere a new ZL1 Mech Cam from Chevy I bought years ago from some Chevy dealer that still stocked them, just never had the heart to use it.
Chevy did re-release the ZL-1 a year or so back as they had them at Jegs and I thought that was hot but when all said and done could do better with a Donavan block and doing it my way. Then a few months ago again the 'never seen before release' of the ZL-1 announced (sarcastic). I think it is a low compression hydro-roller version but still nice 'crate' package.
Here's a link to the new one with some specs -
Motorator Blog - GM's Limited Edition 427 Crate Engine.
Sandy