Material suggestions?

[f350ca]

I've never used a broach so bear with me on this one. If you made the normal sleeve and cut the 3/8 keyway then made another sleeve with the groove cut 7/16, the extra 1/16 to one side, then put a 1/16 spacer in the grove to hold the broach over, then a 1/2 inch sleeve and use a 1/8 spacer. Essentially cut the standard 3/8 keyway then broach out the two sides to get 1/2.
Maybe?