Kelly Jeffrey’s “explosive, high-tempo scoring machine” has created an explosive headache for this seasoned scribe. The Saskatchewan Roughriders’ offence — choreographed by Jeffrey — has become so productive, so quickly, that any attempt to project the final roster without the benefit of a coach’s expertise or a crystal ball is a mind-bending, ultimately futile, process. The pre-season finale was supposed to provide some clarity. So much for that notion. Friday’s 28-16 CFL victory over the host Winnipeg Blue Bombers complicated the already-difficult decisions facing the Roughriders’ coaching staff. All four quarterbacks were effective as the Roughriders won both pre-season games for…