About 20 mins after takeoff the plt reported the right eng had lost power & the acft would not maintain alt. Vectors were provided for an emergency landing, but the acft crashed in a wooded area about 3 mi from the arpt. There was evidence that the gear & flaps had been extended & the acft had entered a turn before impacting. Both props had evidence of low to moderate power & neither was feathered. An exam revealed unsymmetrical wear on the blades of the right turbo-charger; its thrust spacer, PN 406990-9004, was worn & there was evidence of oil leakage. The 13 qt, right eng oil sys had only 6.85 qts of oil remaining. Both turbochargers had been installed during an annual inspection in April 1983 & previously had been overhauled. The acft was estimated to be 844 lbs over its max wt limit & the aft CG limit was exceeded by about 4.8 inches. Six of the passengers were not restrained by seat belts. An associate estimated that the plt had only 4 to 6 hrs of rest in the previous 3 to 4 days.