Engine misfiring and stumbling

[Leecbr]

Hey guys, I know this is not a new topic. I appologise in advance if this is redundant.

I have a 351 windsor with a 4 barrel holley carb. Msd distributor, Msd box, and Msd wires. Also new Holley blue fuel pump ( electtric ). New Starter was installed this year. My spark plugs are clean too.

So here is my situation. My car ran perfect all year no problems. I had it dynoed and tuned last year.
I added lucas gas treatment stuff to it last friday ( september 30 ) and filled the gas. It was rainy all this past week until this past friday ( october 7th ) when I started it and drove it with no issues. After sitting a week due to rainy weather.

It ran perfect until saturday ( october 8th ) morning when I started it. It had a really rough start and idle...Even with the manual choke... I figured maybe colder temps and humidity...

When I started driving, it was stumbling and started to misfire alot. Dunno how this could of happened overnight. I had an old Mallory ignition coil so I changed it out for a msd 3 blaster coil. It ran better but still stumbled a bit and had random misfire mostly in second gear. 3rd and 4th gear ran horrible also.

Could my Msd 6 multispark box be going too. I am somewhat mechanicaly inclined but electrical isn't my thing. Is the Msd distributor bad and possibly threw out the timing.

The cobra was built in 1994 so these parts may very well have been on it since then. I don't know for sure. It only has 28,000 miles on it.

Will the car crap out overnight like this if these items are starting to fail? Or does it not start at all when they begin to fail.

I'm new at this and learning along the way. Any advice will be greatly appreciated.

Thanks,

Lee