Don't know the length, but unsure how that would cause slop. The rod length just determines where the brake pedal sits off the floor. Check if your car has a 2 to 4 bolt adapter plate to mount the alum MC, because that can change the effective length.
All manual MC brake rods should have a rubber bushing at their grooved end that holds the rod inside the MC piston. I have seen the bushings for sale, but perhaps you could fab a solution with an O-ring or plumbing washer. I think the purpose of the rubber is to keep the rod from rattling, though it does lock it tight, making the rod very hard to remove in older cars, maybe because the rubber hardened.
