Those adapters can go up to at least 2 TB. The 1.5/3 stuff you saw is Gbps - speed, not capacity.
If your newer Mac only has IDE, get an IDE-SATA adapter so you can get data onto the drive first, then move the drive back.
If your newer Mac only has IDE, get an IDE-SATA adapter so you can get data onto the drive first, then move the drive back.