Try Randy at Engines Limited (www.engineslimited.com); he may have a 519 block with a casting date that works for your '61, but he won't have a matching VIN and suffix (at least an original one).
Randy for Engines limited recently helped me with my engine block specific needs. He's reliable and honest. In my opinion, you can't go wrong working with him on meeting your special needs. Bill
Art
283 Engine Block 
Linear Mode
