LA 360 Internal Coolant Leak

Let me guess: Holley carb or clone.....

White smoke & losing coolant: will be an internal coolant leak that can be hard to find. Compression test may not reveal anything. Can also be heat related, such as a crack in the bore that gets bigger when the engine heats up; crack/pinhole in intake port or combustion chamber; blown head gasket. Etc.
Edelbrock AVS2 650. Tearing everything apart next week. Checking valve assembly, head gaskets, heads, cylinders, etc. Only real way to see what's going on at this point. What has be scratching my head is that after the compression test, coolant pressure test and cleaning and spacing the spark plugs, it fired right up and idled like a champ after several startups. However, as soon as I put it in gear the RPM's dropped substantially, carb popped and died. This happened every single time putting it in gear.