Are you saying you can turn the 5.125" retainer clear down to the 4.354" size?
I was told you had to enlarge the stock 4.354" hole in the bell housing to work with the 4.805" size retainer. Then you could either swap retainers or turn down the larger retainer to 4.805". Did the factory use a bell housing with a 4.805" register on a small block?