Bunch of differences between the 87 and 88-92 engines.
Crank balancer (88+ has a lip on the magneto side)
Crank balancer oil seal (88+ has a bigger ID for the balancer lip)
Clutch cover (engine number 110185+ are different somehow, but the older one supersedes to it, so it can't be THAT different)
Clutch cover gasket (91+ is a different material)
Magneto cover gasket (91+ is a different material)
Sprocket cover bolt (flanged on 88+)
Sprocket cover bolt lock washers (not used on 88+)
Sprocket cover bolt washers (not used on 88+)
Piston (88+ has a semicircular intake cutaway)
Piston pin bearing washer (88+ has smaller ID to avoid breaking, a MUST for ALL QuadRacers)
Crankshaft assembly (88+ is made of several different parts)
RH crankshaft (88+ is a full circle with 4 holes in it)
LH crankshaft (88+ is a full circle with 4 holes in it)
Cylinder head (88+ has different internal specs)
Cylinder head gasket (88+ is different somehow, 91+ is a different material)
Spark plug (88+ use a B9EGV)
Cylinder (88+ has different internal specs and a different design intake/boost port)
Base gasket (91+ is a different material)
Exhaust valve cover gasket (91+ is a different material)
Reed valve assembly (88+ use a small 6 pedal)
Reed valve stoppers (88+ use small 6 pedal)
Reed valves (88+ use small 6 pedal)
Reed screws (88+ use 6)
Reed valve gasket (88+ use it)
Reed valve bolts (88+ use 6)
Intake manifold (88+ use a 6 bolt)
Gasket set (88+ are different, 91+ gaskets are a different material, includes different o-ring)
Exhaust valve spring (91+ is different somehow)
Exhaust valve holder internal O-ring (91+ is different somehow)
Gear shifting lever (91+ is different somehow, deals with the footguards)
Kick starter shaft (91+ is different somehow, but the older one supersedes to it, so it can't be THAT different)
Kick starter lever (91+ is different somehow, but the older one supersedes to it, so it can't be THAT different)
2nd drive gear (92 is different somehow, but the older one supersedes to it, so it can't be THAT different)
2nd driven gear (91+ is different somehow, but the older one supersedes to it, so it can't be THAT different)
3rd driven gear (91+ is different somehow, but the older one supersedes to it, so it can't be THAT different)