can the valve stem seals be replaced without taking off the head?

youll have to support the valves like that^, and you'll need to get the expensive valve spring tool to compress the valve springs when removing and installing everything. why do you want to replace the valve stem seals?

yes as above ..the seals can be replaced on the engine with a few tool.. a spring compressor..a "air pressure" tool that fits on the spark plug hole and pressurizes the combustion chamber to keep the valves from falling while you remove the springs..or...With a cylinder half way up on it's compression stroke (both valves closed) remove spark plug and feed clothes line into the cylinder letting it trail out the plug hole. Older flimsy stuff works best because it conforms to the combustion chamber better. Continue the compression stroke until it locks. You can now compress and remove valve springs without them dropping. Crank backwards to lower piston, remove the line, move to next cylinder.

Because it is smoke I’d oil out the exhaust

Can you remove cam sprockets without removing cover??