slant six cranks but won't start

Yes it should run with one bad or weak cylinder.

Fule pump sounds fine and basic carb function seems oK since you are getting fuel fouling on the plugs. Clenn the plugs with some carb or brake cleaner or alcohol and chekc the gap while you are at it.

You can do the following tests in the order presented before or after the compression test. I would do these first, as you have a fundamental firing problem that needs to be solved before getting too far with diagnosing one weak cylinder.

Please do the following: Take the spark wire from the distributor and put a philips screweriver in the end and pay it up on the engine so that the sxcredrive balde is about 1/4" form metal; the purpose is to set up a gap of about a 1/4' and then crank it and see if the spark will jump that gap with a blue spark. If it does, then your ignition and spark during cranking is good.

Then take some of the gas you pumped out and smell it; does it smell like fresh gas or does it have an acrid, dog-piss kind of smell? If the latter, then the old bad gas is still in there. (BTW, the bad gas, if not gotten out, could have gummed up a valve in a cylinder...).

Regardless of the smell of the gas, and IF the spark is good, then set the choke butterfly on the carb open and pour a small capful of gas down the carb throat, and then jump in the car, and without touching the gas pedal, try cranking and see if it starts or at least fires a bit. If so, then the carb and/or gas is the problem.

Please do this in the above order and report what you find.

And BTW, fore the cmpresoisn test:
1) remove all the plugs
2) make sure the tester seals against the cylinder head for each test
3) crank the engine over 5-6 times (about 3-4 seonds) and stop and take a reading on that cylinder; release the reading on the guage, and test again; do it twice for each cylinder
4) not having compression tested one of these in a while, I would expect something in the range of 140 psi +/- but the most imporant factor is that cylinders are fairly close to each other
5) please report the readings on each cylinder here