What engine is this part two...

So I think I've got it.  After much contorting and hyper-extending my knees I found what I think is the block casting number up by the back of the block, on the passenger side.  At first I thought it read 800887, when I put in Y4 for the engine code here: http://www.wallaceracing.com/enginesearch4.htm I found a corresponding block code of 500557 for a '77 with a Y4 engine code.

I guess it must be 500557, which would make sense since my car is supposed to have the 400 in it, but damn, that number is a pain to read...

What engine do I have?

So I'm trying to figure out exactly what I have in the car.  According to the sticker and build sheet it should be a 400, but I can't seem to find the code on the block...  Best I can find is the Y4 shown below, but that doesn't correspond to any engine in the '77s I can find online.  I guess not knowing the history of the car is one of those endearing quirks of vehicles that have been played with for 30 years...