[classical glass]

Hi everyone, I'm looking at a Factory 5 cobra and the owner states that it's a 427 side oiler with a 428 crank. Well it's decently a 427 side oiler w/2 4s and well built with many goodies. The only grey area is that he states it has a 428 crank installed when the motor was built about 10 months ago. He has all bills and receipts and all looks legitimate and well done. My question is the crank shaft and pulley. The only numbers on the pulley are L 138 664 and the puzzling thing is the harmonic balancer and the pulley are one piece. Any body have any sound input? The engine runs strong with on issues. One other thing he has March aluminum pulleys on the water pump and alternator but not the crank. I asked about it and he stated all that was up to the builder and he honestly didn't know. I tried to contact the builder which since then has major medical issues with no luck.
Thanks