The strange shifting sounds like slightly low fluid. Be sure it's topped up.

The apparent overheating might be from a bad headgasket, or it might be a clogged or clogging radiator (check the fins outside, too -- they pick up leaves 'n stuff), bad water pump, worn or loose belts (unlikely), a collapsing lower hose, or a flakey thermostat.

Does the engine temp quickly drop when you use the heater full blast?

Regarding the extra white smoke -- if you were consuming coolant, then you'd need to occasionaly top up the overflow tank. Do you?

If the body of your '84 is solid, including floorboards, it may be worth restoring. Don't junk it unless the true repair cost is excessive.

(Remember: The devil you know is better than the devil you don't know.)

The light bulb problem in your '89 sounds like the classic "water sloshing inside the lens" situation. Look for evidence of water inside the housing. You might try sealing the lens to prevent water from entering, and I know several people who've drilled tiny drain holes to allow trapped water to escape. On wagons, I've seen rotted spare tire wells allow water splashed upward to shower over the inside of the taillight housings, destroying bulbs daily (to say nothing of the rest of the car).
--
Don Foster (near Cape Cod, MA)