Hi all. I am fixing my ka, so far changed oil + coolant + air filter + 4x spark plugs + ICV

Spark plugs were the biggest b!tch, rusted to hell in the endura engine and wouldn't budge, took days of vinegar + some brake fluid to get them free without snapping, phew! Car is really smooth now, no noises, APART FROM...

Oil is leaking fast, internally i suspect as no external oil leak is viewable or pool collects. When the engine runs it is white smoke at idle which gets worse with revving. Also drips out the exhaust are constant. What I want to know is how likely is it the head gasket that is blown and not the cylinder head, really don't want to get a new cylinder head. Anyway to prove this?

Also am I right in saying the head gasket can be replaced without removing the engine (endura)?

thanks