[jhein]

Originally Posted by 2BadZ

It original came with the 403 Olds, but at some point I switched it to a Pontiac 455 (maybe 73??) I still have that engine sitting around, separated into complete block, heads, and intake separate. Right now it has a 400 Pontiac in it, maybe 76 or 77. (It's been awhile)

The 400 you have is not original to the car and is likely a 557 block, so nothing special. If I was pulling that motor out, I would most likely not put it back in. I'd go with the '73 455 block you have. Unless you're just hoping you can do a minimal refresh of the 400 and get it running without spending a bunch of money.

If you really want to preserve the 400, I agree with everyone who says pull it and open it up. OTOH, if you don't really care about that motor and you just want to see if you can get it to run without killing it, then you could try to flush it. But if I had to bet, I'd bet it won't survive a flush and run.

Just to point out the obvious, in those "will it run" videos, they don't really care if it runs and survives or not. Either way they get the clicks.