Why not take the opportunity to drain it all out and flush the system and install a fresh mixture? But if you've done that recently then you still have to remove most of it because on a 230 - 250 block the water pump sits fairly low in relation to the bottom of the water jacket.
A quick guess is you will need to drain approx 2 gals or slightly more before you won't have it pour out as you pull off the pump.
