I could find no reference to a 8970010 casting code for a chevy block small, big or otherwise.
The code for the engine in my 76 Vette is 3970010 and it can be either 2 or 4 bolt mains. Since mine started life as an L48 I suspect it's a 2 bolt main block and if I have to pull the engine to change cams I'll find out. That casting number was used from 69-79 so it's a pretty common block.