Ok the only blocks that have that casting number C4AE-6015-A are a 64 352 with a 4.00 bore, 390/361/391 with a 4.05 bore and last a 427 with a 4.23 bore. Also the 427 would have crossbolted mains so that would be easy to tell. It could have been a service block possibly for a 406 made out of a 427 block. You can knock out the freeze plugs and gap the wall cores to see. A 17/64" drill bit shank will fit snug between the cores for a 352/390 block. A 13/64" bit for 406 wall cores and some 361/391's. And 8/64" for 427 wall cores. If the block does not have crosbolt mains it might at least have the crossbolt knorbs or bosses present there. The 428 crank will have a IU, IUB or IUA on the 7th counterweight. The C6AE-E rods are nice LeMans rods with capscrews from the 428 SCJ. The crank and rods are worth $1000 for both. The block once you tell me what you find will have a better idea what it is. I'll email someone about the welded MA to get his input as I'm coming up blank. G.