No problem with fabricating your own. But first, be sure that the axle in the alternator mount has zero wobble or you'll have belt alignment problems.
Assuming from your post that you can do some welding, consider reinforcing the one you've got - cut off some at the end and make the whole thing into angle iron with a strap along one side. I'm suggesting this because cutting the curved slot is one step up in fabrication -it takes a plasma cutter
or skill with a torch.
Good luck with it.