AFTER TAKOFF FM RWY 14, THE ACFT WAS SEEN CLIMBING IN A STEEP NOSE HIGH ATTITUDE AT SLOW SPEED. A WITNESS RPRTD IT RCHD AN ALT OF ABT 75' TO 100' & MAINTD THAT ALT FOR APRX 1/2 MI. IT THEN DSCNDD & HIT THE TOPS OF SVRL TREES, THE ROOF OF A HOUSE & THE GND. AFTER COMING TO REST, THE ACFT WAS BADLY DMGD BY FIRE. ONE WITNESS RPRTD THE ENG SPUTTERED AT ABT THE TIME IT HIT THE TREETOPS. ANOTHER INDCD THE ENG WAS CUTTING OUT. A TEARDOWN OF THE ENG REVEALED A NUMBER OF MAINT DISCREPANCIES. MAG TIMING COULD NOT BE CONFIRMED, DUE TO FIRE DMG, BUT THE LEFT MAG WAS ADJUSTED W/I 1/16' OF FULL UP TRAVEL (IN THE ADJUSTMENT SLOT); THE RGT MAG WAS W/I 1/8' OF FULL DWN TRAVEL. THERE WAS NO RECORD OF A MAG INSPN IAW AD 78-09-07 OR COMPLIANCE WITH AD 82-20-01; THE #3T SPRING WAS MISSING FM THE RGT MAG DISTRIBUTOR BLOCK, HYD TAPPETS WERE OF MIXED PARTS, & ONE CONNECTING ROD WAS OF A DIFFERENT WT & PART NO. THE ENG HAD 93 HRS OF FLT TIME SINCE MAJOR OVERHAUL. ALSO, THE DENSITY ALT WAS ABT 3000' & THE ACFT HAD BEEN LOADED NEAR ITS MAX WT LIMIT.