More information on the 1999 ES300 VVT-i Ignition coil fitment:

Your 1999 Lexus ES300 MUST have VVT-i for these coils to be compatible. To find out if your 1999 ES300 has VVT-i, open your hood. You should see the top plastic engine cover will have the letters "VVT-i" in red.

If the cover is missing, another easy way to tell is to look at the front three ignition coils. They should not have spark plug wires connected to them. The non VVT-i ES300 uses three ignition coils with spark plug wires connected to them, and they are completely different than these. The VVT-i ES300 uses 6 individual ignition coils. 

Definition of VVT-i: Variable Valve Timing Intelligence