There are a number of variants of the Boss engine.

DOHC 4V per Cylinder, 9.5:1 compression, 6000 rpm limit

Balanced crank, different pistons rods and bearings, 10.5:1 compression, thicker gudgeon pin, stronger head bolts, better head gaskets, stainless valves, higher lift cams, larger fuel rails and higher flowing injectors, extra knock sensor,

As 290 with new cams, 10.8:1 compression

New cams, 11.0:1 compression, twin plate throttle body, RPM Limit increased to 6500rpm

As 315 with RPM Limit dropped back to 6000rpm

Not covered by this guide.  3V per cylinder with intake variable cam timing.

Increased compression ration