THE ACFT DISAPPEARED FROM RADAR CONTACT WHILE OVER LAKE MICHIGAN. THIS ACFT HAD DEPARTED BALTIMORE MD AT 1142 CDT TO FLYTO MANITOWOC, WI. THE LAST ENROUTE STOP FOR FUEL WAS AT MUSKEGON MI AT 2040 CDT. THE WEATHER WAS VMC BUT THE NIGHT WAS DARK. NO FLT PLAN WAS FILED. THE ACFT IS ASSUMED DESTROYED BECAUSE A PART OF THE ACFT WITH THE DATA PLATE AND SERIAL # AA1-0414 ON IT WAS FOUND ON A REMOTE BEACH OF LAKE MICHIGAN SOUTH OF ARCADIA ON 7/19/83. THE ACFT DEPARTED MUSKEGON AT ABOUT 2110 CDT WITH A FULL LOAD OF FUEL. AT ABOUT 2145 CDT THE PILOT REPORTED BY RADIO THAT HE HAD LOST AN ENGINE CYLINDER AND WAS GOING DOWN. THE EMERGENCY BEACON CODE WAS PICKED UP BY MUSKEGON APPROACH CONTROL AT A POINT ABOUT 55 MILES NORTHWEST OF MUSKEGON. NO ELT SIGNAL WAS HEARD. THE PILOT IS MISSING AND PRESUMED TO BE FATALLY INJURED. THE COASTGUARD SUSPENDED SEARCH AT 1600 CDT ON JULY 10, 1983 PENDING FURTHER DEVELOPMENTS.