What's your advice for getting R and L leg from where they are (different in strength) to where they will perform the same? High reps? Lower intensity (the left is already at a lower intensity, the right is maxed)?
Keep in mind that the single-leg deadlift is an assistance exercise to bring your weaker hamstrings up. It is not a replacement for the squats and deadlifts, which should remain the foundations of your leg workout.
When doing squats/deadlifts, bring your poundage up to the level just before your weaker right leg starts to complain. Then do the single-leg deadlifts - start with low weight/higher reps, then add weight and lower reps as you get better with the exercise. This is an isolation exercise for the hamstrings, though - you aren't going to use anywhere near the weight you use for squats/deadlifts. Keep the poundages/reps the same for both legs. Over several weeks, see if there is any improvement in your right leg as you slowly add more weight to your squats/deadlifts.
But, like Stu said, some differences will always remain. As you increase your overall strength, the differences will matter less.
The tightness/weakness in your right hamstring suggests that it was injured sometime in the past. The foam roller is a great idea to get rid of knots in the muscle due to scar tissue. Keep it up.
Remember that the glutes, not the hamstrings, are the dominant hip extensor. Tight hip flexors can inhibit the glute's hip extension, forcing the hamstrings to work harder than they should. Formerly sedentary people getting involved in a serious leg exercise program find that there are a host of flexibility/stability issues (in the lower back, hips and thighs) that have to be resolved to make progress.
My push isn't explosive off this leg. Neither is explosive under load, but this one especially.
Once you get your right hamstring straightened out, you might want to add some speed/power training to your routine. Standard training doesn't increase explosiveness that much