It depends on some stuff. How many amps do you need? Is it a single belt system running the water pump and alternator? Is the mechanical fuel pump still there or is it gone?

The 60A Denso kit that I've sold for years is a very simple setup that works really well. It also is lighter and smaller than the factory alternator. I'm now switching my personal stuff over to low mount alternators since I'm EFI and don't have a fuel pump. I have low mount kits for 90A or 60A Denso alternators. Both would fit with plenty of room in a big block E body car. I doubt that you need 90A in your car so the 60A is probably the way to go.