Just scored a FREE 400 2 bolt 010 020 3951509 block that came out of a circle track car. Guy lost a rod (Eagle Aluminum?), and it took out a small portion of the bottom of the bores on the camshaft side of the cylinder. I measured, and based on a 3.75" stroke, at BDC, the worse of the two affected cylinders has about 1.125" from the top of the piston down to the damaged area (i.e. missing chunk of metal). The block was stroker clearanced, but I doubt that will work as a stroker anymore... At the very least, if it checked out clean with no cracks, it'd make a heck of a destroked 377 or less!

Would it make a difference if using 5.565" stock 400 rods or the longer 5.7" 350 rods, as far as the damage done? I would think that maybe the longer rods would give it more room to clear the damaged portion?

If it threw a rod I would suspect there is a reason why it did that.

Maybe the block is tweaked.
Before getting my sights set, I'd let a good machine shop look at it before I spent $$$$.

Absolutely. It will be the best money you'll ever spend on this engine. Have it checked out thoroughly, including sonic testing, magnafluxing, and pressure testing at least (although maybe not in that order).

My guess is, if it was still a servicable block, it would be going back in the round-d-round car. You won't know until it's at the machine shop to be checked out. Sometimes it sucks to have to spend money to find out you have a huge paperweight. But a servicable (even if it has to be sleeved) 400 block is worth the risk.

If the cylinder is split and it migrates down into the camshaft area (and into the cooling jacket) it's garbage. It won't be an easy repair and stands a chance of being a leaker even after the repair. Also agreed is if the block was serviceable (with all the $$$ machine work invested) it would still be in the owner's service.

i would be very leary of the block

Make sure that the area that is missing gets cleaned up so that you won't have a spreading crack if you do decide to use it.