They are 1/4" pipe plugs at the bottom of the block. About in the middle. Here's the info from Evanscooling.com.
1. NEVER work on a conventional hot pressurized water/antifreeze cooling system
2. Drain radiator by opening the petcock.
3. Drain the block by removing both block drains
• Drains are ¼” pipe plugs removed with a ¼” drive square ratchet.
• Driver side drain is 3” from rear of block and 2” above oil pan rail.
• Passenger side drain is 4” from rear of block and 2” above oil pan rail. (Clearance is tight with starter. If necessary remove 2 starter bolts and let hang to remove drain.)
4. Remove heater hose from font passenger side cylinder head and blow out with compressed air.
• If equipped with rear heater or heater control valve, disconnect lines at firewall and blow out.
6. Let everything drain for at least 15 minutes.
7. Plug all drains, reconnect heater hose and fill system with Evans NPG+ coolant.