Fluid volume during cooler swap?

[HoveringHMMWV]

Doing some procedural reading for an engine cooler swap and wondering how much fluid loss should be expected. Anyone with experience on this procedure? The TM says to plan on capturing fluid spills. Would it help to just drain engine oil and trans fluid prior?

 

[Mogman]

Basically what is in the coolers, the engine and trans fittings are lower than the cooler so not much will flow out of the lines.