You're right. I miised the Hill part of the post. I'd look at '94 after 44'sand66's They both have heavier Drivetrains. Of course they be more $$$ I got this from Hoober, Inc. - Axial-Flow Combine Timeline 1986 Introduction of 1600 Series Axial-Flow Combines 1620 124 H.P. 358 Cu.In. 125 Bu. Grain Tank 1640 150 H.P. 466 Cu.In. 145 Bu. Grain Tank 1660 180 H.P. 466 Cu.In. 180 Bu. Grain Tank 1680 225 H.P. 466 Cu.In. 210 Bu. Grain Tank Capacity increases of 70% on 1640 and 1660 and 25% on 1680 Increased concave area by 15.5% on 1640 and 1660 and 16% on 1680 Increased separating area by 24% on 1620, 32% on 1640 and 1660, and 41% on 1680 Cage vanes adjustable without removing bolts or concaves and grates Clean grain augers increased in diameter (7" on 1640 and 1660 and 8" on 1680) Deeper clean grain elevator cross section (11.1 x 6" on 1640 and 1660 and 11.1 x 8" on 1680) Tear drop clean grain elevator lower boot Tapered entry design into clean grain elevator boot Inclined delivery auger standard on all 1680s and 1660 rice models Shaft speed monitor standard (monitors 9 areas, two more, feeder and spreader) Improved lighting package (6-60 watt halogen lights including one long distance light) Optional feeder reverser all 1600 (field kits for certain 1400 series) Introduction of 1020 Flexible Cutterbar Header 1.5" knife system standard on 1020 Flx. Optional on 1010 Cross auger lifts with reel lift for reversing 1987 Direction of rotation for rotary air screen reversed Shaft speed monitor made standard Final drive axle changed to one-piece forged shaft 1988 Model number decals were moved up to the front of the combine beside the grain tank Rotor drive pulley improved Slotted bolt holes in concave hanger brackets on RH side 1989 Introduction of New CDC Engines (4_1_89) 1620 145 H.P. 5.9 liter 125 Bu. Grain Tank 1640 160 H.P. 5.9 liter 145 Bu. Grain Tank 1660 190 H.P. 8.3 liter 180 Bu. Grain Tank 1680 235 H.P. 8.3 liter 210 Bu. Grain Tank In-line core radiators replace staggered tupe design 110 amp Bosh alternator replaced 90 amp Motorola with engine deflector shields Battery sizes upgraded Coolant level sensor added Engine aspirator for Navistar engine combines 1990 Audible alarm added to grain-tank full indicator Right side service access door added on 1640_1660 Heavy-duty cleaning system drive parts: sieve hangers, hanger arms, pitmans, and shafts Cab heater valve replaced by valve from 7100 Magnum tractors 1991 High visibility reel released for 1020 Flex and 1010 headers long cleaning system released for 1680-grain combines Dual spin-on hydraulic filters on 1680 Electric fuel transfer pump on 1680 1992 Introduction of Field Tracker 92-120" rear axle standard Fuel line diameter increased to 1_2" and screen eliminated from tank Hydraulic reservoir increased from 5 gallons to 8 gallons New lay-over header lift valve Accumulator standard Auxiliary and reel drive pumps combined into one dual pump Dual spin-on hydraulic filters on 1640_1660 (same as 1680) 2-piece hydrostatic steel lines replaced by a center steel tube with outer rubber hoses with 4-bolt split flange connectors Rotor coupling bolts changed from grade 5 to grade 8 1620 combine discontinued 1993 Introduction of Second Generation 1600 Series Axial-Flow Combines 1644 180 H.P. 5.9 liter 145 Bu. Grain Tank 1666 215 H.P. 8.3 liter 180 Bu. Grain Tank 1688 260 H.P. 8.3 liter 210 Bu. Grain Tank Introduction of Cross-Flow Cleaning Fan long cleaning system (13.75" added to chaffer and shoe sieve) 25.9% 44_66 and 23.7% on 88 larger air cleaners on 1666_1688 Water-pump sealed stalk roll bearings on 1000 series cornheads 1994 Introduction of Straw_Chaff spreader system (factory and field codes for long sieve units) 1644 gets 1666_1688 transmision, final drive, and brakes Optional cold-start package (ether assist and block heater) Electric fuel pump added on 1644_1666 Radial-seal type engine air filters Transition cone and rotor cage seam bolts heads treated with tungsten-carbide Unloading auger spill saver added 1995 Introduction of 2100 Series Axial-Flow Combine 2144 180 H.P. 5.9 liter 145 Bu. Grain Tank 2166 215 H.P. 8.3 liter 180 Bu. Grain Tank 2188 260 H.P. 8.3 liter 210 Bu. Grain Tank All new cab and styling (23% more total glass area than 1600 series) Improved stadium-design lighting New optional lighting package (after cut, side flood, rear work, and service lights) Theater style lay-out to right-hand console Mult-function propulsion lever New A-post instrumentation center Improved operator ladder Focalized cab mounting system New pressure and flow-compensated (PFC) hydraulics and wet brakes New safety shielding, service platforms, hand rails, and guards Improved hinged service panels for easier access AFS field installed AFS systems released (March) 1996 Factory installed AFS systems released (March)