Listen up, Marines! This week’s cover story is a must-read for all — from the lowliest privates to tomorrow’s general officers. Marine Corps Times Pentagon correspondent Andrew Tilghman lays out in stark detail an aggressive new plan to revamp the military retirement system, one that would dump today’s 20-year model in favor of something akin to a corporate 401(k). The proposal, pitched by an influential Pentagon advisory board, calls for everyone to receive at least some retirement cash when they leave the service. Even Marines who complete just one enlistment and get out as lance corporals would clear about $20,000.…