Slant 6 wont start

hmm, progressively worse can be loss of compression, clogged carb, or vacuum leak among other things.
If the previous owner had the car sitting for a while, crap can get stirred up in the tank and sent on to the carb, even through the filter. After a while it's just too much for the thing to run well or at all.
Does it still have the single barrel carb?

You may have to spend some quality time going through everything, just wright down what you are trying to accomplish / fix, do one thing at a time. Don't get side tracked or you'll get it taken too far apart or have 10 things going at once or forget where things were set before you started tinkering :lol: ask me how I know :)