If those are your plugs, they look way past their use by date but I think you have bigger issues. If it smokes continuously under load, I'm calling dead rings/worn cylinder bores. Make sure you do the test correctly or you'll get some misleading results. Main cause of oil burn is bad valve stem seals and the symptom is a cough of smoke on acceleration from a stationary start. If you are hearing air leak from the intake or exhaust it sounds like the valves and valve seats are worn. You may get away with a light deglaze of the cylinder bores and some new rings but you're not going to know until you crack it open. If the head isn't trash a decent old school machine shop can test it and do a valve seat cut and install new valves. Done right and you'll get 10 years out of it easy (if you don't experience any cooling system problems...)