It might be worth checking whether your state offers any financial incentives to offset the cost of replacing an old furnace with a new "greener" one.  It could well be that such incentives are only offered to people of a certain "status", for example having an elderly or incapacitated person in the household, but it would be worth asking the question because a subsidy might bring the cost of replacement into the realm of affordability.

Picture 3 it shows it's full of dirt and sand.
I wouldn't even think twice on replacing it. I believe that model has a 20-25 year life cycle.

Don't mess around faulty furnaces can be dangerous.

One issue that others with intimate knowledge of the North American furnaces can comment on is that of the exhaust flue.  Old systems in the UK used air from the room to combust with the gas and expelled it through a single-walled flue.  Houses had to have air vents in the walls to allow fresh air to be replenished.  A lot of people blocked those vents and sealed teir doors and windows against draughts, but this resulted in valuable oxygen in the house being gradually used up.

This has happened here in the US as well. Code requires adequate air flow to the unit, but when we bought our current house, many of the crawl space vents were indeed blocked. After an inspection, they said there was still plenty of air flow, but it was a good idea to check.  They did require a carbon dioxide detector to be installed in the room adjacent to the furnace to be sure the unit was not filling the house with CO2, which thankfully has never gone off.

As for the life of a furnace, I have done quite a bit of research on this. If you use your furnace quite often all year round, 25 years is about the right time to replace it.  But here in California we use it not very often. Our mid70s unit was just inspected (we do it yearly) by someone who sells new units. He told me that there was 10+ years life left, it was running at 80%+ efficiency, while a new unit in our price (4 to 5k) range would only be 85%+ efficient, so we might as well wait. ( The super efficient ones were $8000 to $10000!)

My suggestion is to disregard us all, as our OPINIONS are going to vary. Pay the money to have it inspected by a professional.  They can clean it at the same time to keep it running and tell you if it needs replacement. If it needs to be replaced, get multiple bids, and make them detail what is included. I suspect with a unit that old that duct work will also be needed, as well as bringing the space up to current code, which can add “surprise” costs at install time. Ask a lot of questions.  We noted that estimates varied all over the place, so some research into heater units might be worth while too.  

Good luck

BTW: This time of year many companies offer cleaning and inspection services.  Check them out online before taking one of those offers. Many are often a scam to tell you you need hundreds of dollars of unneeded work and do little cleaning or repair.

Check Yelp and your local Nectdoor for recommendations.

Thanks guys.   Did a bunch of a troubleshooting today.  Eliminated all the components.  Except the valve.  See attached.
Now the issue is to find these same valves is almost impossible.  Need to look for something compatible.  

Any ideas what could be the same vertical fit as this valve?
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That valve is what kills the gas to the heater if the pilot goes out. It uses a thermocouple to detect that the pilot is lit, and keep the gas on as long as the copper tube going to the pilot stays hot. Otherwise, it will kill the gas to the heater to keep it from leaking into the house if the pilot gets blown out.  It can also be used to turn off the gas.

There should be a red knob on the top that has positions for OFF, ON, and LIGHT.

Any competent heater repair company can replace it with a newer compatible valve.  It will look something like this:

https://www.ebay.com/bhp/furnace-gas-valve

Hope that helps.

thanks again Owen.  i'm looking for a compatible valve that can replace mine.  I think orientation is important.  mine connects vertically to the input output gas.

Actually, orientation is not really important. When they replaced mine last time, the added one of those flexible hoses to the gas line to attach to the new valve.  This is what mine looks like now:

very similar valve to mine.   I was cautious and thought some valve can only designed to work vertically,  other horizontally.  I could be wrong tho.

I am not sure. I believe all the ones I have seen are mounted as I see mine. Again, you may wish to discuss this with a professional, or look at some specs on valves to see what they say.

Thank you Tiras25.

Thank you all!