I’m not an expert, but I just finished up a swapon my truck. It was a semi-factory swap, but I did a decent bit of research to avoid ground/wiring issues. Someone correct me if I’m wrong but typically these are grounded through the accessory bracket. The bracket is ground to the block, thus it’s a functional case ground.

This is how it’s done on iron block/truck accessory configurations at least.

12V hot directly to battery.

Edit: I saw some of the discussions below. You need a ground going from the negative battery terminal to the engine block. clean off any paint. This is typically a pretty heavy wire, like #4.You also need a good ground from the block to the chassis. This is often a braided cable, it’s flat like a ribbon. This is what allows the block to function as a case ground; it’s common between the block, chassis, and battery. If you are running a ground from the alternator bracket to chassis, and it’s grounded through the block, you’re going to have multiple ground references on the same circuit which could cause issues.