Bomelia Befor you go crazy do a couple of things. 1st A 4.13 bore could be a 406 or a 428 engine if stock. Send it to a machinist that knows FE blocks and have him sonic all 8 cylinders and check for cracks in the block. magaflux it. SEE WHAT YOU HAVE. Check to see if the block is still aligned and square. The crank throws are what makes the displacement of the motor. From 352 to 428 they all take the same lenght rods. If the block is OK, keep it. If not send it back. Call E-Bay and find out about a return. You didn't say the price but you can always sleave the block. This is why buying sight unseen problems happen. What are the Mic readings?? You can take a 428, 30 over and be OK. I wouldn't do 7000 rpms with it. Do the basics with the block as fast as you can and call E-Bay. You didn't say what you where building your car for?? Racing,parades,orginiallity, or fun. A FE in acobra is still an FE. Cubes where from 390 to 428 from Shel himself. Take a breath and Check it out
You may have a diamond in the rough. Let us know what happens. Rick Lake