1966 0lds 425 Engine Problem

[TODD RUBIN]

1.  The engine was sitting for a year or less, and was run 3x while parked in December '05 all was fine! 2.   Started it yesterday and the engine was "missing" like a shake while in idle. 3.   In December I added high test 2 gals. gas with small amount of lead additive. 4.   Added 4 gals more of gas as it was out of gas yesterday 5.   Any ideas of what to check to correct this? (I checked the spark across each plugs on the cap,  the spark was there on all 8.)   thanks,   Todd