Apparently so. Think this one came out of a full size Chebbie station wagon, possibly a 71 or 72. I have not candled the block number all that closely in recent memory. Side loading could prove to be a problem; I would need a good bore gauge and a bit of quiet time to run the cylinders and see just how bad things are. Biggest issue with the 400 is that those siamesed cylinder sleeves severely limit the possible overbore; .030 is about the practical max as I recall.
As for the steam holes, While, as suggested, any "good" cylinder could do as a core or starting point, the actual drilling is not so straight forward. Those holes do not get drilled at a 90 degree or perpendicular angle to the gasket face. They must be both specifically sited to intersect with the coolant passages in the head and must do so at a specific angle of intersection; all while staying in alignment with the matching holes in the deck of the block. If any parameter is out of alignment then the holes will land misaligned and the heads will be ruined. This is not a job that I would trust to either of my local machine shops; I would almost be forced to seek out a race engine shop and hope they have an opening and a machinist with multiple decades of experience and expertise (There is A Difference) in doing these heads as well as owning a beard so long and grey that he can tuck it in his belt!!
Nick
