May Need Battery Terminals/Cable Ends Cleaned, Sounds Like It's Not Getting A Good Connection. Probably Be Better Off Just Cleaning The Battery Terminals And Putting New Terminal Ends On Your Existing Cables...Ya, The Squeek Sounds Like A U-Joint Like You Said. As Far As An Easy Way To Change The Spark Plugs, Pay Someone Else To Do It...LoL J/K.
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Mustangs,,, It's Whats For Dinner